Method and device for image encoding/decoding, and recording medium having bitstream stored thereon

ABSTRACT

Disclosed in a method of decoding an image. The method includes determining a zero out region within a current block; partitioning a region except for the zero out region within the current block, on a per transform coefficient group basis; and decoding a transform coefficient on the per transform coefficient group basis.

TECHNICAL FIELD

The present invention relates to a method and apparatus forencoding/decoding image and recording medium for storing bitstream. Inparticular, the present invention relates to an improved transformcoefficient encoding/decoding method.

BACKGROUND ART

Recently, demands for high-resolution and high-quality images such ashigh definition (HD) images and ultra-high definition (UHD) images haveincreased in various application fields. However, higher resolution andquality image data has increasing amounts of data in comparison withconventional image data. Therefore, when transmitting image data byusing a medium such as conventional wired and wireless broadbandnetworks, or when storing image data by using a conventional storagemedium, costs of transmitting and storing increase. In order to solvethese problems occurring with an increase in resolution and quality ofimage data, a high-efficiency image encoding/decoding technique for animage with high-resolution and high image quality is required.

Image compression techniques include various techniques, such as aninter prediction technique of predicting a pixel value included in acurrent picture from the preceding or following picture of the currentpicture, an intra prediction technique of predicting a pixel valueincluded in a current picture by using pixel information within thecurrent picture, transform and quantization techniques for compressingthe energy of a residual signal, an entropy encoding technique ofassigning a short code to a value with a high appearance frequency andof assigning a long code to a value with a low appearance frequency, andthe like. These image compression techniques are used to compress imagedata effectively for transmission or storage.

In video encoding/decoding, a residual signal resulting from predictionencoding is transformed into a frequency domain, and a coefficientthereof is quantized to obtain a transform coefficient, and thenencoding/decoding is performed on the transform coefficient. Intransform coefficient encoding, various techniques are used: a transformcoefficient grouping technique for determining a coding unit of atransform coefficient; a transform coefficient scanning technique forarranging coefficients of a transform coefficient group processed in a2D form into a 1D form; and a transform coefficient binarization andentropy encoding technique for binary encoding coefficient valuesarranged in one dimension and representing the resulting values into abit string for final storage and transmission.

For effective encoding of the transform coefficients, transformcoefficient grouping, which can well reflect the values of the transformcoefficients generated and the distribution characteristic, and atransform coefficient scanning method are required. However, in therelated art, the same scanning method is applied to a transformcoefficient group in a fixed size and to a transform coefficient groupwithin a coding block, so that there is a limit of the performance inencoding the transform coefficients.

Also, according to a quantization parameter and the positions of thetransform coefficients, the values of the transform coefficients vary insize. However, in the related art, only one transform coefficientbinarization method which is relatively effective in the case where thevalues of the transform coefficients are small is applied, so that thereis a limit of the performance in encoding the transform coefficients.

In the related art, to encode a transform coefficient of a currentcoding block, a coding block is divided into transform coefficientgroups in a fixed size, and the transform coefficient groups resultingfrom the division are subjected to transform coefficient encoding usingthe same scanning method. Since within one coding block, the samescanning method applied to the transform coefficient group in the samesize is applied, there is a limit in that the distributioncharacteristic of the transform coefficients within the coding block isnot adaptively reflected.

According to an applied quantization parameter and the positions of thetransform coefficients within a transform block, the values of thetransform coefficients generated vary in size. When the value of thequantization parameter is small due to the characteristics of an imageor the transform coefficient corresponds to a low frequency component ofthe image, the value of the transform coefficient is large. However, inthe related art, the method of binary encoding the transform coefficientmainly considers the case where the values of the transform coefficientsare not large. Thus, a transform coefficient binarization method thatcan well reflect the case where the values of the transform coefficientsare large is required.

DISCLOSURE Technical Problem

The present invention is intended to adaptively and flexibly configure atransform coefficient grouping, which is a unit of transform coefficientencoding, and a transform coefficient scanning method.

Also, the present invention is intended to propose a binarization methodthat is capable of well representing a transform coefficient in a casewhere a value of a transform coefficient is large, compared to theconventional transform coefficient binarization method.

Technical Solution

A method of decoding an image according to the present invention, themethod may comprise determining a zero out region within a currentblock, partitioning a region except for the zero out region within thecurrent block, on a per transform coefficient group basis and decoding atransform coefficient on the per transform coefficient group basis.

In the method of decoding an image according to the present invention,wherein at the determining of the zero out region, when a width or aheight of the current block is larger than a first predefined size, aregion of which a size is equal to or larger than the first predefinedsize within the current block is determined to be the zero out region.

In the method of decoding an image according to the present invention,wherein at the determining of the zero out region, the determining isbased on a type of frequency transform of the current block.

In the method of decoding an image according to the present invention,wherein at the determining of the zero out region, when a type offrequency transform of the current block is DST-7 or DCT-8, a region ofwhich a size is equal to or larger than a second predefined size withinthe current block is determined to be the zero out region.

In the method of decoding an image according to the present invention,wherein at the determining of the zero out region, when a type offrequency transform of the current block is DCT-2, a region of which asize is equal to or larger than a third predefined size within thecurrent block is determined to be the zero out region.

In the method of decoding an image according to the present invention,wherein a size of the transform coefficient group is determined on thebasis of a width and a height of the current block.

In the method of decoding an image according to the present invention,wherein when a width or a height of the current block is smaller than afourth predefined size, a size of the transform coefficient group isdetermined to be a fifth predefined size, and when the width and theheight of the current block is larger than the fourth predefined size,the size of the transform coefficient group is determined to be a sixthpredefined size, wherein the sixth predefined size is larger than thefifth predefined size.

In the method of decoding an image according to the present invention,wherein a shape of the transform coefficient group is determined to be anon-square shape when an area of the current block is larger than apredefined area and a shape of the current block is a non-square shape.

A method of encoding an image according to the present invention, themethod may comprise determining a zero out region within a currentblock, partitioning a region except for the zero out region within thecurrent block, on a per transform coefficient group basis and encoding atransform coefficient on the per transform coefficient group basis.

In the method of encoding an image according to the present invention,wherein at the determining of the zero out region, when a width or aheight of the current block is larger than a first predefined size, aregion of which a size is equal to or larger than the first predefinedsize within the current block is determined to be the zero out region.

In the method of encoding an image according to the present invention,wherein at the determining of the zero out region, the determining isbased on a type of frequency transform of the current block.

In the method of encoding an image according to the present invention,wherein at the determining of the zero out region, when a type offrequency transform of the current block is DST-7 or DCT-8, a region ofwhich a size is equal to or larger than a second predefined size withinthe current block is determined to be the zero out region.

In the method of encoding an image according to the present invention,wherein at the determining of the zero out region, when a type offrequency transform of the current block is DCT-2, a region of which asize is equal to or larger than a third predefined size within thecurrent block is determined to be the zero out region.

In the method of encoding an image according to the present invention,wherein a size of the transform coefficient group is determined on thebasis of a width and a height of the current block.

In the method of encoding an image according to the present invention,wherein when a width or a height of the current block is smaller than afourth predefined size, a size of the transform coefficient group isdetermined to be a fifth predefined size, and when the width and theheight of the current block is larger than the fourth predefined size,the size of the transform coefficient group is determined to be a sixthpredefined size, wherein the sixth predefined size is larger than thefifth predefined size.

In the method of encoding an image according to the present invention,wherein a shape of the transform coefficient group is determined to be anon-square shape when an area of the current block is larger than apredefined area and a shape of the current block is a non-square shape.

Advantageous Effects

The present invention proposes transform coefficient groups in varioussizes within a coding block and different scanning methods for therespective transform coefficient groups so that highly flexibletransform coefficient grouping and transform coefficient scanning arepossible, and proposes an effective binarization method for a transformcoefficient having a large value so that much effective transformcoefficient encoding is possible.

The present invention can reduce the number of transform coefficientsthat need to be encoded through efficient transform coefficient groupingand scanning methods.

The present invention can perform efficient binarization in which atransform coefficient of which a value is large is assigned relativelyfew binary bits.

According to the present invention, image encoding and decodingefficiency can be enhanced.

According to the present invention, the computational complexity of animage encoder and an image decoder can be reduced.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration according to anexample of an encoding apparatus to which the present invention applies.

FIG. 2 is a block diagram illustrating a configuration according to anexample of a decoding apparatus to which the present invention applies.

FIG. 3 is a diagram schematically illustrating a partitioning structureof an image when encoding and decoding the image.

FIG. 4 is a diagram illustrating an example of an intra predictionprocess.

FIG. 5 is a diagram illustrating an example of an inter predictionprocess.

FIG. 6 is a diagram illustrating transform and quantization processes.

FIG. 7 is a diagram illustrating reference samples available for intraprediction.

FIG. 8 is a diagram illustrating filtering for block boundaries adjacentto each other according to an embodiment of the present invention.

FIGS. 9 to 12 are diagrams illustrating an example of fixed blocktransform coefficient grouping of the present invention.

FIGS. 13 to 15 are diagrams illustrating an example of variable blocktransform coefficient grouping of the present invention.

FIG. 16 is a diagram illustrating a method of determining a transformcoefficient group on the basis of a position of a non-zero transformcoefficient within a current block.

FIGS. 17 to 20 are diagrams illustrating how to determine a transformcoefficient grouping method on the basis of a width (M) or a height (N)of a current block (M×N).

FIGS. 21 to 23 are diagrams illustrating a method of setting a transformcoefficient group by using an intra prediction mode and positioninformation of the last non-zero coefficient.

FIGS. 24 and 25 are diagrams illustrating a zero out region and anon-zero out region according to an embodiment of the present invention.

FIGS. 26 and 27 are diagrams illustrating transform coefficient groupingin a non-zero out region.

FIG. 28 is a diagram illustrating examples of a fixed transformcoefficient scanning method.

FIG. 29 is a diagram illustrating a transform coefficient presenceindicator based on a transform coefficient and a transform coefficientpresence indicator based on a transform coefficient group.

FIG. 30 is a diagram illustrating transform coefficient binarizationbased on absolute value comparison.

FIG. 31 is a diagram illustrating transform coefficient binarizationbased on exponential scale comparison.

FIG. 32 is a flowchart illustrating a method of decoding an imageaccording to an embodiment of the present invention.

MODE FOR INVENTION

A variety of modifications may be made to the present invention andthere are various embodiments of the present invention, examples ofwhich will now be provided with reference to drawings and described indetail. However, the present invention is not limited thereto, althoughthe exemplary embodiments can be construed as including allmodifications, equivalents, or substitutes in a technical concept and atechnical scope of the present invention. The similar reference numeralsrefer to the same or similar functions in various aspects. In thedrawings, the shapes and dimensions of elements may be exaggerated forclarity. In the following detailed description of the present invention,references are made to the accompanying drawings that show, by way ofillustration, specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to implement the present disclosure. Itshould be understood that various embodiments of the present disclosure,although different, are not necessarily mutually exclusive. For example,specific features, structures, and characteristics described herein, inconnection with one embodiment, may be implemented within otherembodiments without departing from the spirit and scope of the presentdisclosure. In addition, it should be understood that the location orarrangement of individual elements within each disclosed embodiment maybe modified without departing from the spirit and scope of the presentdisclosure. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present disclosure isdefined only by the appended claims, appropriately interpreted, alongwith the full range of equivalents to what the claims claim.

Terms used in the specification, ‘first’, ‘second’, etc. can be used todescribe various components, but the components are not to be construedas being limited to the terms. The terms are only used to differentiateone component from other components. For example, the ‘first’ componentmay be named the ‘second’ component without departing from the scope ofthe present invention, and the ‘second’ component may also be similarlynamed the ‘first’ component. The term ‘and/or’ includes a combination ofa plurality of items or any one of a plurality of terms.

It will be understood that when an element is simply referred to asbeing ‘connected to’ or ‘coupled to’ another element without being‘directly connected to’ or ‘directly coupled to’ another element in thepresent description, it may be ‘directly connected to’ or ‘directlycoupled to’ another element or be connected to or coupled to anotherelement, having the other element intervening therebetween. In contrast,it should be understood that when an element is referred to as being“directly coupled” or “directly connected” to another element, there areno intervening elements present.

Furthermore, constitutional parts shown in the embodiments of thepresent invention are independently shown so as to representcharacteristic functions different from each other. Thus, it does notmean that each constitutional part is constituted in a constitutionalunit of separated hardware or software. In other words, eachconstitutional part includes each of enumerated constitutional parts forconvenience. Thus, at least two constitutional parts of eachconstitutional part may be combined to form one constitutional part orone constitutional part may be divided into a plurality ofconstitutional parts to perform each function. The embodiment where eachconstitutional part is combined and the embodiment where oneconstitutional part is divided are also included in the scope of thepresent invention, if not departing from the essence of the presentinvention.

The terms used in the present specification are merely used to describeparticular embodiments, and are not intended to limit the presentinvention. An expression used in the singular encompasses the expressionof the plural, unless it has a clearly different meaning in the context.In the present specification, it is to be understood that terms such as“including”, “having”, etc. are intended to indicate the existence ofthe features, numbers, steps, actions, elements, parts, or combinationsthereof disclosed in the specification, and are not intended to precludethe possibility that one or more other features, numbers, steps,actions, elements, parts, or combinations thereof may exist or may beadded. In other words, when a specific element is referred to as being“included”, elements other than the corresponding element are notexcluded, but additional elements may be included in embodiments of thepresent invention or the scope of the present invention.

In addition, some of constituents may not be indispensable constituentsperforming essential functions of the present invention but be selectiveconstituents improving only performance thereof. The present inventionmay be implemented by including only the indispensable constitutionalparts for implementing the essence of the present invention except theconstituents used in improving performance. The structure including onlythe indispensable constituents except the selective constituents used inimproving only performance is also included in the scope of the presentinvention.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. In describingexemplary embodiments of the present invention, well-known functions orconstructions will not be described in detail since they mayunnecessarily obscure the understanding of the present invention. Thesame constituent elements in the drawings are denoted by the samereference numerals, and a repeated description of the same elements willbe omitted.

Hereinafter, an image may mean a picture configuring a video, or maymean the video itself. For example, “encoding or decoding or both of animage” may mean “encoding or decoding or both of a moving picture”, andmay mean “encoding or decoding or both of one image among images of amoving picture.”

Hereinafter, terms “moving picture” and “video” may be used as the samemeaning and be replaced with each other.

Hereinafter, a target image may be an encoding target image which is atarget of encoding and/or a decoding target image which is a target ofdecoding. Also, a target image may be an input image inputted to anencoding apparatus, and an input image inputted to a decoding apparatus.Here, a target image may have the same meaning with the current image.

Hereinafter, terms “image”, “picture, “frame” and “screen” may be usedas the same meaning and be replaced with each other.

Hereinafter, a target block may be an encoding target block which is atarget of encoding and/or a decoding target block which is a target ofdecoding. Also, a target block may be the current block which is atarget of current encoding and/or decoding. For example, terms “targetblock” and “current block” may be used as the same meaning and bereplaced with each other.

Hereinafter, terms “block” and “unit” may be used as the same meaningand be replaced with each other. Or a “block” may represent a specificunit.

Hereinafter, terms “region” and “segment” may be replaced with eachother.

Hereinafter, a specific signal may be a signal representing a specificblock. For example, an original signal may be a signal representing atarget block. A prediction signal may be a signal representing aprediction block. A residual signal may be a signal representing aresidual block.

In embodiments, each of specific information, data, flag, index, elementand attribute, etc. may have a value. A value of information, data,flag, index, element and attribute equal to “0” may represent a logicalfalse or the first predefined value. In other words, a value “0”, afalse, a logical false and the first predefined value may be replacedwith each other. A value of information, data, flag, index, element andattribute equal to “1” may represent a logical true or the secondpredefined value. In other words, a value “1”, a true, a logical trueand the second predefined value may be replaced with each other.

When a variable i or j is used for representing a column, a row or anindex, a value of i may be an integer equal to or greater than 0, orequal to or greater than 1. That is, the column, the row, the index,etc. may be counted from 0 or may be counted from 1.

DESCRIPTION OF TERMS

Encoder: means an apparatus performing encoding. That is, means anencoding apparatus.

Decoder: means an apparatus performing decoding. That is, means andecoding apparatus.

Block: is an M×N array of a sample. Herein, M and N may mean positiveintegers, and the block may mean a sample array of a two-dimensionalform. The block may refer to a unit. A current block my mean an encodingtarget block that becomes a target when encoding, or a decoding targetblock that becomes a target when decoding. In addition, the currentblock may be at least one of an encode block, a prediction block, aresidual block, and a transform block.

Sample: is a basic unit constituting a block. It may be expressed as avalue from 0 to 2Bd−1 according to a bit depth (Bd). In the presentinvention, the sample may be used as a meaning of a pixel. That is, asample, a pel, a pixel may have the same meaning with each other.

Unit: may refer to an encoding and decoding unit. When encoding anddecoding an image, the unit may be a region generated by partitioning asingle image. In addition, the unit may mean a subdivided unit when asingle image is partitioned into subdivided units during encoding ordecoding. That is, an image may be partitioned into a plurality ofunits. When encoding and decoding an image, a predetermined process foreach unit may be performed. A single unit may be partitioned intosub-units that have sizes smaller than the size of the unit. Dependingon functions, the unit may mean a block, a macroblock, a coding treeunit, a code tree block, a coding unit, a coding block), a predictionunit, a prediction block, a residual unit), a residual block, atransform unit, a transform block, etc. In addition, in order todistinguish a unit from a block, the unit may include a luma componentblock, a chroma component block associated with the luma componentblock, and a syntax element of each color component block. The unit mayhave various sizes and forms, and particularly, the form of the unit maybe a two-dimensional geometrical figure such as a square shape, arectangular shape, a trapezoid shape, a triangular shape, a pentagonalshape, etc. In addition, unit information may include at least one of aunit type indicating the coding unit, the prediction unit, the transformunit, etc., and a unit size, a unit depth, a sequence of encoding anddecoding of a unit, etc.

Coding Tree Unit: is configured with a single coding tree block of aluma component Y, and two coding tree blocks related to chromacomponents Cb and Cr. In addition, it may mean that including the blocksand a syntax element of each block. Each coding tree unit may bepartitioned by using at least one of a quad-tree partitioning method, abinary-tree partitioning method and ternary-tree partitioning method toconfigure a lower unit such as coding unit, prediction unit, transformunit, etc. It may be used as a term for designating a sample block thatbecomes a process unit when encoding/decoding an image as an inputimage. Here, the quad-tree may mean a quarternary-tree.

When the size of the coding block is within a predetermined range, thedivision is possible using only quad-tree partitioning. Here, thepredetermined range may be defined as at least one of a maximum size anda minimum size of a coding block in which the division is possible usingonly quad-tree partitioning. Information indicating a maximum/minimumsize of a coding block in which quad-tree partitioning is allowed may besignaled through a bitstream, and the information may be signaled in atleast one unit of a sequence, a picture parameter, a tile group, or aslice (segment). Alternatively, the maximum/minimum size of the codingblock may be a fixed size predetermined in the coder/decoder. Forexample, when the size of the coding block corresponds to 256×256 to64×64, the division is possible only using quad-tree partitioning.Alternatively, when the size of the coding block is larger than the sizeof the maximum conversion block, the division is possible only usingquad-tree partitioning. Herein, the block to be divided may be at leastone of a coding block and a transform block. In this case, informationindicating the division of the coded block (for example, split_flag) maybe a flag indicating whether or not to perform the quad-treepartitioning. When the size of the coding block falls within apredetermined range, the division is possible only using binary tree orternary tree partitioning. In this case, the above description of thequad-tree partitioning may be applied to binary tree partitioning orternary tree partitioning in the same manner.

Coding Tree Block: may be used as a term for designating any one of a Ycoding tree block, Cb coding tree block, and Cr coding tree block.

Neighbor Block: may mean a block adjacent to a current block. The blockadjacent to the current block may mean a block that comes into contactwith a boundary of the current block, or a block positioned within apredetermined distance from the current block. The neighbor block maymean a block adjacent to a vertex of the current block. Herein, theblock adjacent to the vertex of the current block may mean a blockvertically adjacent to a neighbor block that is horizontally adjacent tothe current block, or a block horizontally adjacent to a neighbor blockthat is vertically adjacent to the current block.

Reconstructed Neighbor block: may mean a neighbor block adjacent to acurrent block and which has been already spatially/temporally encoded ordecoded. Herein, the reconstructed neighbor block may mean areconstructed neighbor unit. A reconstructed spatial neighbor block maybe a block within a current picture and which has been alreadyreconstructed through encoding or decoding or both. A reconstructedtemporal neighbor block is a block at a corresponding position as thecurrent block of the current picture within a reference image, or aneighbor block thereof.

Unit Depth: may mean a partitioned degree of a unit. In a treestructure, the highest node (Root Node) may correspond to the first unitwhich is not partitioned. Also, the highest node may have the leastdepth value. In this case, the highest node may have a depth of level 0.A node having a depth of level 1 may represent a unit generated bypartitioning once the first unit. A node having a depth of level 2 mayrepresent a unit generated by partitioning twice the first unit. A nodehaving a depth of level n may represent a unit generated by partitioningn-times the first unit. A Leaf Node may be the lowest node and a nodewhich cannot be partitioned further. A depth of a Leaf Node may be themaximum level. For example, a predefined value of the maximum level maybe 3. A depth of a root node may be the lowest and a depth of a leafnode may be the deepest. In addition, when a unit is expressed as a treestructure, a level in which a unit is present may mean a unit depth.

Bitstream: may mean a bitstream including encoding image information.

Parameter Set: corresponds to header information among a configurationwithin a bitstream. At least one of a video parameter set, a sequenceparameter set, a picture parameter set, and an adaptation parameter setmay be included in a parameter set. In addition, a parameter set mayinclude a slice header, a tile group header, and tile headerinformation. The term “tile group” means a group of tiles and has thesame meaning as a slice.

Parsing: may mean determination of a value of a syntax element byperforming entropy decoding, or may mean the entropy decoding itself.

Symbol: may mean at least one of a syntax element, a coding parameter,and a transform coefficient value of an encoding/decoding target unit.In addition, the symbol may mean an entropy encoding target or anentropy decoding result.

Prediction Mode: may be information indicating a mode encoded/decodedwith intra prediction or a mode encoded/decoded with inter prediction.

Prediction Unit: may mean a basic unit when performing prediction suchas inter-prediction, intra-prediction, inter-compensation,intra-compensation, and motion compensation. A single prediction unitmay be partitioned into a plurality of partitions having a smaller size,or may be partitioned into a plurality of lower prediction units. Aplurality of partitions may be a basic unit in performing prediction orcompensation. A partition which is generated by dividing a predictionunit may also be a prediction unit.

Prediction Unit Partition: may mean a form obtained by partitioning aprediction unit.

Reference picture list may refer to a list including one or morereference pictures used for inter prediction or motion compensation.There are several types of usable reference picture lists, including LC(List combined), L0 (List 0), L1 (List 1), L2 (List 2), L3 (List 3).

Inter prediction indicator may refer to a direction of inter prediction(unidirectional prediction, bidirectional prediction, etc.) of a currentblock. Alternatively, it may refer to the number of reference picturesused to generate a prediction block of a current block. Alternatively,it may refer to the number of prediction blocks used at the time ofperforming inter prediction or motion compensation on a current block.

Prediction list utilization flag indicates whether a prediction block isgenerated using at least one reference picture in a specific referencepicture list. An inter prediction indicator can be derived using aprediction list utilization flag, and conversely, a prediction listutilization flag can be derived using an inter prediction indicator. Forexample, when the prediction list utilization flag has a first value ofzero (0), it means that a reference picture in a reference picture listis not used to generate a prediction block. On the other hand, when theprediction list utilization flag has a second value of one (1), it meansthat a reference picture list is used to generate a prediction block.

Reference picture index may refer to an index indicating a specificreference picture in a reference picture list.

Reference picture may mean a reference picture which is referred to by aspecific block for the purposes of inter prediction or motioncompensation of the specific block. Alternatively, the reference picturemay be a picture including a reference block referred to by a currentblock for inter prediction or motion compensation. Hereinafter, theterms “reference picture” and “reference image” have the same meaningand can be interchangeably.

Motion vector may be a two-dimensional vector used for inter predictionor motion compensation. The motion vector may mean an offset between anencoding/decoding target block and a reference block. For example, (mvX,mvY) may represent a motion vector. Here, mvX may represent a horizontalcomponent and mvY may represent a vertical component.

Search range may be a two-dimensional region which is searched toretrieve a motion vector during inter prediction. For example, the sizeof the search range may be M×N. Here, M and N are both integers.

Motion vector candidate may refer to a prediction candidate block or amotion vector of the prediction candidate block when predicting a motionvector. In addition, a motion vector candidate may be included in amotion vector candidate list.

Motion vector candidate list may mean a list composed of one or moremotion vector candidates.

Motion vector candidate index may mean an indicator indicating a motionvector candidate in a motion vector candidate list. Alternatively, itmay be an index of a motion vector predictor.

Motion information may mean information including at least one of theitems including a motion vector, a reference picture index, an interprediction indicator, a prediction list utilization flag, referencepicture list information, a reference picture, a motion vectorcandidate, a motion vector candidate index, a merge candidate, and amerge index.

Merge candidate list may mean a list composed of one or more mergecandidates.

Merge candidate may mean a spatial merge candidate, a temporal mergecandidate, a combined merge candidate, a combined bi-predictive mergecandidate, or a zero merge candidate. The merge candidate may includemotion information such as an inter prediction indicator, a referencepicture index for each list, a motion vector, a prediction listutilization flag, and an inter prediction indicator.

Merge index may mean an indicator indicating a merge candidate in amerge candidate list. Alternatively, the merge index may indicate ablock from which a merge candidate has been derived, among reconstructedblocks spatially/temporally adjacent to a current block. Alternatively,the merge index may indicate at least one piece of motion information ofa merge candidate.

Transform Unit: may mean a basic unit when performing encoding/decodingsuch as transform, inverse-transform, quantization, dequantization,transform coefficient encoding/decoding of a residual signal. A singletransform unit may be partitioned into a plurality of lower-leveltransform units having a smaller size. Here,transformation/inverse-transformation may comprise at least one amongthe first transformation/the first inverse-transformation and the secondtransformation/the second inverse-transformation.

Scaling: may mean a process of multiplying a quantized level by afactor. A transform coefficient may be generated by scaling a quantizedlevel. The scaling also may be referred to as dequantization.

Quantization Parameter: may mean a value used when generating aquantized level using a transform coefficient during quantization. Thequantization parameter also may mean a value used when generating atransform coefficient by scaling a quantized level duringdequantization. The quantization parameter may be a value mapped on aquantization step size.

Delta Quantization Parameter: may mean a difference value between apredicted quantization parameter and a quantization parameter of anencoding/decoding target unit.

Scan: may mean a method of sequencing coefficients within a unit, ablock or a matrix. For example, changing a two-dimensional matrix ofcoefficients into a one-dimensional matrix may be referred to asscanning, and changing a one-dimensional matrix of coefficients into atwo-dimensional matrix may be referred to as scanning or inversescanning.

Transform Coefficient: may mean a coefficient value generated aftertransform is performed in an encoder. It may mean a coefficient valuegenerated after at least one of entropy decoding and dequantization isperformed in a decoder. A quantized level obtained by quantizing atransform coefficient or a residual signal, or a quantized transformcoefficient level also may fall within the meaning of the transformcoefficient.

Quantized Level: may mean a value generated by quantizing a transformcoefficient or a residual signal in an encoder. Alternatively, thequantized level may mean a value that is a dequantization target toundergo dequantization in a decoder. Similarly, a quantized transformcoefficient level that is a result of transform and quantization alsomay fall within the meaning of the quantized level.

Non-zero Transform Coefficient: may mean a transform coefficient havinga value other than zero, or a transform coefficient level or a quantizedlevel having a value other than zero.

Quantization Matrix: may mean a matrix used in a quantization process ora dequantization process performed to improve subjective or objectiveimage quality. The quantization matrix also may be referred to as ascaling list.

Quantization Matrix Coefficient: may mean each element within aquantization matrix. The quantization matrix coefficient also may bereferred to as a matrix coefficient.

Default Matrix: may mean a predetermined quantization matrixpreliminarily defined in an encoder or a decoder.

Non-default Matrix: may mean a quantization matrix that is notpreliminarily defined in an encoder or a decoder but is signaled by auser.

Statistic Value: a statistic value for at least one among a variable, anencoding parameter, a constant value, etc. which have a computablespecific value may be one or more among an average value, a sum value, aweighted average value, a weighted sum value, the minimum value, themaximum value, the most frequent value, a median value, an interpolatedvalue of the corresponding specific values.

FIG. 1 is a block diagram showing a configuration of an encodingapparatus according to an embodiment to which the present invention isapplied.

An encoding apparatus 100 may be an encoder, a video encoding apparatus,or an image encoding apparatus. A video may include at least one image.The encoding apparatus 100 may sequentially encode at least one image.

Referring to FIG. 1, the encoding apparatus 100 may include a motionprediction unit 111, a motion compensation unit 112, an intra-predictionunit 120, a switch 115, a subtractor 125, a transform unit 130, aquantization unit 140, an entropy encoding unit 150, a dequantizationunit 160, an inverse-transform unit 170, an adder 175, a filter unit180, and a reference picture buffer 190.

The encoding apparatus 100 may perform encoding of an input image byusing an intra mode or an inter mode or both. In addition, encodingapparatus 100 may generate a bitstream including encoded informationthrough encoding the input image, and output the generated bitstream.The generated bitstream may be stored in a computer readable recordingmedium, or may be streamed through a wired/wireless transmission medium.When an intra mode is used as a prediction mode, the switch 115 may beswitched to an intra. Alternatively, when an inter mode is used as aprediction mode, the switch 115 may be switched to an inter mode.Herein, the intra mode may mean an intra-prediction mode, and the intermode may mean an inter-prediction mode. The encoding apparatus 100 maygenerate a prediction block for an input block of the input image. Inaddition, the encoding apparatus 100 may encode a residual block using aresidual of the input block and the prediction block after theprediction block being generated. The input image may be called as acurrent image that is a current encoding target. The input block may becalled as a current block that is current encoding target, or as anencoding target block.

When a prediction mode is an intra mode, the intra-prediction unit 120may use a sample of a block that has been already encoded/decoded and isadjacent to a current block as a reference sample. The intra-predictionunit 120 may perform spatial prediction for the current block by using areference sample, or generate prediction samples of an input block byperforming spatial prediction. Herein, the intra prediction may meanintra-prediction.

When a prediction mode is an inter mode, the motion prediction unit 111may retrieve a region that best matches with an input block from areference image when performing motion prediction, and deduce a motionvector by using the retrieved region. In this case, a search region maybe used as the region. The reference image may be stored in thereference picture buffer 190. Here, when encoding/decoding for thereference image is performed, it may be stored in the reference picturebuffer 190.

The motion compensation unit 112 may generate a prediction block byperforming motion compensation for the current block using a motionvector. Herein, inter-prediction may mean inter-prediction or motioncompensation.

When the value of the motion vector is not an integer, the motionprediction unit 111 and the motion compensation unit 112 may generatethe prediction block by applying an interpolation filter to a partialregion of the reference picture. In order to perform inter-pictureprediction or motion compensation on a coding unit, it may be determinedthat which mode among a skip mode, a merge mode, an advanced motionvector prediction (AMVP) mode, and a current picture referring mode isused for motion prediction and motion compensation of a prediction unitincluded in the corresponding coding unit. Then, inter-pictureprediction or motion compensation may be differently performed dependingon the determined mode.

The subtractor 125 may generate a residual block by using a differenceof an input block and a prediction block. The residual block may becalled as a residual signal. The residual signal may mean a differencebetween an original signal and a prediction signal. In addition, theresidual signal may be a signal generated by transforming or quantizing,or transforming and quantizing a difference between the original signaland the prediction signal. The residual block may be a residual signalof a block unit.

The transform unit 130 may generate a transform coefficient byperforming transform of a residual block, and output the generatedtransform coefficient. Herein, the transform coefficient may be acoefficient value generated by performing transform of the residualblock. When a transform skip mode is applied, the transform unit 130 mayskip transform of the residual block.

A quantized level may be generated by applying quantization to thetransform coefficient or to the residual signal. Hereinafter, thequantized level may be also called as a transform coefficient inembodiments.

The quantization unit 140 may generate a quantized level by quantizingthe transform coefficient or the residual signal according to aparameter, and output the generated quantized level. Herein, thequantization unit 140 may quantize the transform coefficient by using aquantization matrix.

The entropy encoding unit 150 may generate a bitstream by performingentropy encoding according to a probability distribution on valuescalculated by the quantization unit 140 or on coding parameter valuescalculated when performing encoding, and output the generated bitstream.The entropy encoding unit 150 may perform entropy encoding of sampleinformation of an image and information for decoding an image. Forexample, the information for decoding the image may include a syntaxelement.

When entropy encoding is applied, symbols are represented so that asmaller number of bits are assigned to a symbol having a high chance ofbeing generated and a larger number of bits are assigned to a symbolhaving a low chance of being generated, and thus, the size of bit streamfor symbols to be encoded may be decreased. The entropy encoding unit150 may use an encoding method for entropy encoding such as exponentialGolomb, context-adaptive variable length coding (CAVLC),context-adaptive binary arithmetic coding (CABAC), etc. For example, theentropy encoding unit 150 may perform entropy encoding by using avariable length coding/code (VLC) table. In addition, the entropyencoding unit 150 may deduce a binarization method of a target symboland a probability model of a target symbol/bin, and perform arithmeticcoding by using the deduced binarization method, and a context model.

In order to encode a transform coefficient level (quantized level), theentropy encoding unit 150 may change a two-dimensional block formcoefficient into a one-dimensional vector form by using a transformcoefficient scanning method.

A coding parameter may include information (flag, index, etc.) such assyntax element that is encoded in an encoder and signaled to a decoder,and information derived when performing encoding or decoding. The codingparameter may mean information required when encoding or decoding animage. For example, at least one value or a combination form of aunit/block size, a unit/block depth, unit/block partition information,unit/block shape, unit/block partition structure, whether to partitionof a quad-tree form, whether to partition of a binary-tree form, apartition direction of a binary-tree form (horizontal direction orvertical direction), a partition form of a binary-tree form (symmetricpartition or asymmetric partition), whether or not a current coding unitis partitioned by ternary tree partitioning, direction (horizontal orvertical direction) of the ternary tree partitioning, type (symmetric orasymmetric type) of the ternary tree partitioning, whether a currentcoding unit is partitioned by multi-type tree partitioning, direction(horizontal or vertical direction) of the multi-type three partitioning,type (symmetric or asymmetric type) of the multi-type tree partitioning,and a tree (binary tree or ternary tree) structure of the multi-typetree partitioning, a prediction mode(intra prediction or interprediction), a luma intra-prediction mode/direction, a chromaintra-prediction mode/direction, intra partition information, interpartition information, a coding block partition flag, a prediction blockpartition flag, a transform block partition flag, a reference samplefiltering method, a reference sample filter tab, a reference samplefilter coefficient, a prediction block filtering method, a predictionblock filter tap, a prediction block filter coefficient, a predictionblock boundary filtering method, a prediction block boundary filter tab,a prediction block boundary filter coefficient, an intra-predictionmode, an inter-prediction mode, motion information, a motion vector, amotion vector difference, a reference picture index, a inter-predictionangle, an inter-prediction indicator, a prediction list utilizationflag, a reference picture list, a reference picture, a motion vectorpredictor index, a motion vector predictor candidate, a motion vectorcandidate list, whether to use a merge mode, a merge index, a mergecandidate, a merge candidate list, whether to use a skip mode, aninterpolation filter type, an interpolation filter tab, an interpolationfilter coefficient, a motion vector size, a presentation accuracy of amotion vector, a transform type, a transform size, information ofwhether or not a primary (first) transform is used, information ofwhether or not a secondary transform is used, a primary transform index,a secondary transform index, information of whether or not a residualsignal is present, a coded block pattern, a coded block flag (CBF), aquantization parameter, a quantization parameter residue, a quantizationmatrix, whether to apply an intra loop filter, an intra loop filtercoefficient, an intra loop filter tab, an intra loop filter shape/form,whether to apply a deblocking filter, a deblocking filter coefficient, adeblocking filter tab, a deblocking filter strength, a deblocking filtershape/form, whether to apply an adaptive sample offset, an adaptivesample offset value, an adaptive sample offset category, an adaptivesample offset type, whether to apply an adaptive loop filter, anadaptive loop filter coefficient, an adaptive loop filter tab, anadaptive loop filter shape/form, a binarization/inverse-binarizationmethod, a context model determining method, a context model updatingmethod, whether to perform a regular mode, whether to perform a bypassmode, a context bin, a bypass bin, a significant coefficient flag, alast significant coefficient flag, a coded flag for a unit of acoefficient group, a position of the last significant coefficient, aflag for whether a value of a coefficient is larger than 1, a flag forwhether a value of a coefficient is larger than 2, a flag for whether avalue of a coefficient is larger than 3, information on a remainingcoefficient value, a sign information, a reconstructed luma sample, areconstructed chroma sample, a residual luma sample, a residual chromasample, a luma transform coefficient, a chroma transform coefficient, aquantized luma level, a quantized chroma level, a transform coefficientlevel scanning method, a size of a motion vector search area at adecoder side, a shape of a motion vector search area at a decoder side,a number of time of a motion vector search at a decoder side,information on a CTU size, information on a minimum block size,information on a maximum block size, information on a maximum blockdepth, information on a minimum block depth, an imagedisplaying/outputting sequence, slice identification information, aslice type, slice partition information, tile identificationinformation, a tile type, tile partition information, tile groupidentification information, a tile group type, tile group partitioninformation, a picture type, a bit depth of an input sample, a bit depthof a reconstruction sample, a bit depth of a residual sample, a bitdepth of a transform coefficient, a bit depth of a quantized level, andinformation on a luma signal or information on a chroma signal may beincluded in the coding parameter.

Herein, signaling the flag or index may mean that a corresponding flagor index is entropy encoded and included in a bitstream by an encoder,and may mean that the corresponding flag or index is entropy decodedfrom a bitstream by a decoder.

When the encoding apparatus 100 performs encoding throughinter-prediction, an encoded current image may be used as a referenceimage for another image that is processed afterwards. Accordingly, theencoding apparatus 100 may reconstruct or decode the encoded currentimage, or store the reconstructed or decoded image as a reference imagein reference picture buffer 190.

A quantized level may be dequantized in the dequantization unit 160, ormay be inverse-transformed in the inverse-transform unit 170. Adequantized or inverse-transformed coefficient or both may be added witha prediction block by the adder 175. By adding the dequantized orinverse-transformed coefficient or both with the prediction block, areconstructed block may be generated. Herein, the dequantized orinverse-transformed coefficient or both may mean a coefficient on whichat least one of dequantization and inverse-transform is performed, andmay mean a reconstructed residual block.

A reconstructed block may pass through the filter unit 180. The filterunit 180 may apply at least one of a deblocking filter, a sampleadaptive offset (SAO), and an adaptive loop filter (ALF) to areconstructed sample, a reconstructed block or a reconstructed image.The filter unit 180 may be called as an in-loop filter.

The deblocking filter may remove block distortion generated inboundaries between blocks. In order to determine whether or not to applya deblocking filter, whether or not to apply a deblocking filter to acurrent block may be determined based samples included in several rowsor columns which are included in the block. When a deblocking filter isapplied to a block, another filter may be applied according to arequired deblocking filtering strength.

In order to compensate an encoding error, a proper offset value may beadded to a sample value by using a sample adaptive offset. The sampleadaptive offset may correct an offset of a deblocked image from anoriginal image by a sample unit. A method of partitioning samples of animage into a predetermined number of regions, determining a region towhich an offset is applied, and applying the offset to the determinedregion, or a method of applying an offset in consideration of edgeinformation on each sample may be used.

The adaptive loop filter may perform filtering based on a comparisonresult of the filtered reconstructed image and the original image.Samples included in an image may be partitioned into predeterminedgroups, a filter to be applied to each group may be determined, anddifferential filtering may be performed for each group. Information ofwhether or not to apply the ALF may be signaled by coding units (CUs),and a form and coefficient of the ALF to be applied to each block mayvary.

The reconstructed block or the reconstructed image having passed throughthe filter unit 180 may be stored in the reference picture buffer 190. Areconstructed block processed by the filter unit 180 may be a part of areference image. That is, a reference image is a reconstructed imagecomposed of reconstructed blocks processed by the filter unit 180. Thestored reference image may be used later in inter prediction or motioncompensation.

FIG. 2 is a block diagram showing a configuration of a decodingapparatus according to an embodiment and to which the present inventionis applied.

A decoding apparatus 200 may a decoder, a video decoding apparatus, oran image decoding apparatus.

Referring to FIG. 2, the decoding apparatus 200 may include an entropydecoding unit 210, a dequantization unit 220, an inverse-transform unit230, an intra-prediction unit 240, a motion compensation unit 250, anadder 225, a filter unit 260, and a reference picture buffer 270.

The decoding apparatus 200 may receive a bitstream output from theencoding apparatus 100. The decoding apparatus 200 may receive abitstream stored in a computer readable recording medium, or may receivea bitstream that is streamed through a wired/wireless transmissionmedium. The decoding apparatus 200 may decode the bitstream by using anintra mode or an inter mode. In addition, the decoding apparatus 200 maygenerate a reconstructed image generated through decoding or a decodedimage, and output the reconstructed image or decoded image.

When a prediction mode used when decoding is an intra mode, a switch maybe switched to an intra. Alternatively, when a prediction mode used whendecoding is an inter mode, a switch may be switched to an inter mode.

The decoding apparatus 200 may obtain a reconstructed residual block bydecoding the input bitstream, and generate a prediction block. When thereconstructed residual block and the prediction block are obtained, thedecoding apparatus 200 may generate a reconstructed block that becomes adecoding target by adding the reconstructed residual block with theprediction block. The decoding target block may be called a currentblock.

The entropy decoding unit 210 may generate symbols by entropy decodingthe bitstream according to a probability distribution. The generatedsymbols may include a symbol of a quantized level form. Herein, anentropy decoding method may be an inverse-process of the entropyencoding method described above.

In order to decode a transform coefficient level (quantized level), theentropy decoding unit 210 may change a one-directional vector formcoefficient into a two-dimensional block form by using a transformcoefficient scanning method.

A quantized level may be dequantized in the dequantization unit 220, orinverse-transformed in the inverse-transform unit 230. The quantizedlevel may be a result of dequantizing or inverse-transforming or both,and may be generated as a reconstructed residual block. Herein, thedequantization unit 220 may apply a quantization matrix to the quantizedlevel.

When an intra mode is used, the intra-prediction unit 240 may generate aprediction block by performing, for the current block, spatialprediction that uses a sample value of a block adjacent to a decodingtarget block and which has been already decoded.

When an inter mode is used, the motion compensation unit 250 maygenerate a prediction block by performing, for the current block, motioncompensation that uses a motion vector and a reference image stored inthe reference picture buffer 270.

The adder 225 may generate a reconstructed block by adding thereconstructed residual block with the prediction block. The filter unit260 may apply at least one of a deblocking filter, a sample adaptiveoffset, and an adaptive loop filter to the reconstructed block orreconstructed image. The filter unit 260 may output the reconstructedimage. The reconstructed block or reconstructed image may be stored inthe reference picture buffer 270 and used when performinginter-prediction. A reconstructed block processed by the filter unit 260may be a part of a reference image. That is, a reference image is areconstructed image composed of reconstructed blocks processed by thefilter unit 260. The stored reference image may be used later in interprediction or motion compensation.

FIG. 3 is a view schematically showing a partition structure of an imagewhen encoding and decoding the image. FIG. 3 schematically shows anexample of partitioning a single unit into a plurality of lower units.

In order to efficiently partition an image, when encoding and decoding,a coding unit (CU) may be used. The coding unit may be used as a basicunit when encoding/decoding the image. In addition, the coding unit maybe used as a unit for distinguishing an intra prediction mode and aninter prediction mode when encoding/decoding the image. The coding unitmay be a basic unit used for prediction, transform, quantization,inverse-transform, dequantization, or an encoding/decoding process of atransform coefficient.

Referring to FIG. 3, an image 300 is sequentially partitioned in alargest coding unit (LCU), and a LCU unit is determined as a partitionstructure. Herein, the LCU may be used in the same meaning as a codingtree unit (CTU). A unit partitioning may mean partitioning a blockassociated with to the unit. In block partition information, informationof a unit depth may be included. Depth information may represent anumber of times or a degree or both in which a unit is partitioned. Asingle unit may be partitioned into a plurality of lower level unitshierarchically associated with depth information based on a treestructure. In other words, a unit and a lower level unit generated bypartitioning the unit may correspond to a node and a child node of thenode, respectively. Each of partitioned lower unit may have depthinformation. Depth information may be information representing a size ofa CU, and may be stored in each CU. Unit depth represents times and/ordegrees related to partitioning a unit. Therefore, partitioninginformation of a lower-level unit may comprise information on a size ofthe lower-level unit.

A partition structure may mean a distribution of a coding unit (CU)within an LCU 310. Such a distribution may be determined according towhether or not to partition a single CU into a plurality (positiveinteger equal to or greater than 2 including 2, 4, 8, 16, etc.) of CUs.A horizontal size and a vertical size of the CU generated bypartitioning may respectively be half of a horizontal size and avertical size of the CU before partitioning, or may respectively havesizes smaller than a horizontal size and a vertical size beforepartitioning according to a number of times of partitioning. The CU maybe recursively partitioned into a plurality of CUs. By the recursivepartitioning, at least one among a height and a width of a CU afterpartitioning may decrease comparing with at least one among a height anda width of a CU before partitioning. Partitioning of the CU may berecursively performed until to a predefined depth or predefined size.For example, a depth of an LCU may be 0, and a depth of a smallestcoding unit (SCU) may be a predefined maximum depth. Herein, the LCU maybe a coding unit having a maximum coding unit size, and the SCU may be acoding unit having a minimum coding unit size as described above.Partitioning is started from the LCU 310, a CU depth increases by 1 as ahorizontal size or a vertical size or both of the CU decreases bypartitioning. For example, for each depth, a CU which is not partitionedmay have a size of 2N×2N. Also, in case of a CU which is partitioned, aCU with a size of 2N×2N may be partitioned into four CUs with a size ofN×N. A size of N may decrease to half as a depth increase by 1.

In addition, information whether or not the CU is partitioned may berepresented by using partition information of the CU. The partitioninformation may be 1-bit information. All CUs, except for a SCU, mayinclude partition information. For example, when a value of partitioninformation is a first value, the CU may not be partitioned, when avalue of partition information is a second value, the CU may bepartitioned

Referring to FIG. 3, an LCU having a depth 0 may be a 64×64 block. 0 maybe a minimum depth. A SCU having a depth 3 may be an 8×8 block. 3 may bea maximum depth. A CU of a 32×32 block and a 16×16 block may berespectively represented as a depth 1 and a depth 2.

For example, when a single coding unit is partitioned into four codingunits, a horizontal size and a vertical size of the four partitionedcoding units may be a half size of a horizontal and vertical size of theCU before being partitioned. In one embodiment, when a coding unithaving a 32×32 size is partitioned into four coding units, each of thefour partitioned coding units may have a 16×16 size. When a singlecoding unit is partitioned into four coding units, it may be called thatthe coding unit may be partitioned into a quad-tree form.

For example, when one coding unit is partitioned into two sub-codingunits, the horizontal or vertical size (width or height) of each of thetwo sub-coding units may be half the horizontal or vertical size of theoriginal coding unit. For example, when a coding unit having a size of32×32 is vertically partitioned into two sub-coding units, each of thetwo sub-coding units may have a size of 16×32. For example, when acoding unit having a size of 8×32 is horizontally partitioned into twosub-coding units, each of the two sub-coding units may have a size of8×16. When one coding unit is partitioned into two sub-coding units, itcan be said that the coding unit is binary-partitioned or is partitionedby a binary tree partition structure.

For example, when one coding unit is partitioned into three sub-codingunits, the horizontal or vertical size of the coding unit can bepartitioned with a ratio of 1:2:1, thereby producing three sub-codingunits whose horizontal or vertical sizes are in a ratio of 1:2:1. Forexample, when a coding unit having a size of 16×32 is horizontallypartitioned into three sub-coding units, the three sub-coding units mayhave sizes of 16×8, 16×16, and 16×8 respectively, in the order from theuppermost to the lowermost sub-coding unit. For example, when a codingunit having a size of 32×32 is vertically split into three sub-codingunits, the three sub-coding units may have sizes of 8×32, 16×32, and8×32, respectively in the order from the left to the right sub-codingunit. When one coding unit is partitioned into three sub-coding units,it can be said that the coding unit is ternary-partitioned orpartitioned by a ternary tree partition structure.

In FIG. 3, a coding tree unit (CTU) 320 is an example of a CTU to whicha quad tree partition structure, a binary tree partition structure, anda ternary tree partition structure are all applied.

As described above, in order to partition the CTU, at least one of aquad tree partition structure, a binary tree partition structure, and aternary tree partition structure may be applied. Various tree partitionstructures may be sequentially applied to the CTU, according to apredetermined priority order. For example, the quad tree partitionstructure may be preferentially applied to the CTU. A coding unit thatcannot be partitioned any longer using a quad tree partition structuremay correspond to a leaf node of a quad tree. A coding unitcorresponding to a leaf node of a quad tree may serve as a root node ofa binary and/or ternary tree partition structure. That is, a coding unitcorresponding to a leaf node of a quad tree may be further partitionedby a binary tree partition structure or a ternary tree partitionstructure, or may not be further partitioned. Therefore, by preventing acoding block that results from binary tree partitioning or ternary treepartitioning of a coding unit corresponding to a leaf node of a quadtree from undergoing further quad tree partitioning, block partitioningand/or signaling of partition information can be effectively performed.

The fact that a coding unit corresponding to a node of a quad tree ispartitioned may be signaled using quad partition information. The quadpartition information having a first value (e.g., “1”) may indicate thata current coding unit is partitioned by the quad tree partitionstructure. The quad partition information having a second value (e.g.,“0”) may indicate that a current coding unit is not partitioned by thequad tree partition structure. The quad partition information may be aflag having a predetermined length (e.g., one bit).

There may not be a priority between the binary tree partitioning and theternary tree partitioning. That is, a coding unit corresponding to aleaf node of a quad tree may further undergo arbitrary partitioningamong the binary tree partitioning and the ternary tree partitioning. Inaddition, a coding unit generated through the binary tree partitioningor the ternary tree partitioning may undergo a further binary treepartitioning or a further ternary tree partitioning, or may not befurther partitioned.

A tree structure in which there is no priority among the binary treepartitioning and the ternary tree partitioning is referred to as amulti-type tree structure. A coding unit corresponding to a leaf node ofa quad tree may serve as a root node of a multi-type tree. Whether topartition a coding unit which corresponds to a node of a multi-type treemay be signaled using at least one of multi-type tree partitionindication information, partition direction information, and partitiontree information. For partitioning of a coding unit corresponding to anode of a multi-type tree, the multi-type tree partition indicationinformation, the partition direction, and the partition tree informationmay be sequentially signaled.

The multi-type tree partition indication information having a firstvalue (e.g., “1”) may indicate that a current coding unit is to undergoa multi-type tree partitioning. The multi-type tree partition indicationinformation having a second value (e.g., “0”) may indicate that acurrent coding unit is not to undergo a multi-type tree partitioning.

When a coding unit corresponding to a node of a multi-type tree isfurther partitioned by a multi-type tree partition structure, the codingunit may include partition direction information. The partitiondirection information may indicate in which direction a current codingunit is to be partitioned for the multi-type tree partitioning. Thepartition direction information having a first value (e.g., “1”) mayindicate that a current coding unit is to be vertically partitioned. Thepartition direction information having a second value (e.g., “0”) mayindicate that a current coding unit is to be horizontally partitioned.

When a coding unit corresponding to a node of a multi-type tree isfurther partitioned by a multi-type tree partition structure, thecurrent coding unit may include partition tree information. Thepartition tree information may indicate a tree partition structure whichis to be used for partitioning of a node of a multi-type tree. Thepartition tree information having a first value (e.g., “1”) may indicatethat a current coding unit is to be partitioned by a binary treepartition structure. The partition tree information having a secondvalue (e.g., “0”) may indicate that a current coding unit is to bepartitioned by a ternary tree partition structure.

The partition indication information, the partition tree information,and the partition direction information may each be a flag having apredetermined length (e.g., one bit).

At least any one of the quadtree partition indication information, themulti-type tree partition indication information, the partitiondirection information, and the partition tree information may be entropyencoded/decoded. For the entropy-encoding/decoding of those types ofinformation, information on a neighboring coding unit adjacent to thecurrent coding unit may be used. For example, there is a highprobability that the partition type (the partitioned or non-partitioned,the partition tree, and/or the partition direction) of a leftneighboring coding unit and/or an upper neighboring coding unit of acurrent coding unit is similar to that of the current coding unit.Therefore, context information for entropy encoding/decoding of theinformation on the current coding unit may be derived from theinformation on the neighboring coding units. The information on theneighboring coding units may include at least any one of quad partitioninformation, multi-type tree partition indication information, partitiondirection information, and partition tree information.

As another example, among binary tree partitioning and ternary treepartitioning, binary tree partitioning may be preferentially performed.That is, a current coding unit may primarily undergo binary treepartitioning, and then a coding unit corresponding to a leaf node of abinary tree may be set as a root node for ternary tree partitioning. Inthis case, neither quad tree partitioning nor binary tree partitioningmay not be performed on the coding unit corresponding to a node of aternary tree.

A coding unit that cannot be partitioned by a quad tree partitionstructure, a binary tree partition structure, and/or a ternary treepartition structure becomes a basic unit for coding, prediction and/ortransformation. That is, the coding unit cannot be further partitionedfor prediction and/or transformation. Therefore, the partition structureinformation and the partition information used for partitioning a codingunit into prediction units and/or transformation units may not bepresent in a bit stream.

However, when the size of a coding unit (i.e., a basic unit forpartitioning) is larger than the size of a maximum transformation block,the coding unit may be recursively partitioned until the size of thecoding unit is reduced to be equal to or smaller than the size of themaximum transformation block. For example, when the size of a codingunit is 64×64 and when the size of a maximum transformation block is32×32, the coding unit may be partitioned into four 32×32 blocks fortransformation. For example, when the size of a coding unit is 32×64 andthe size of a maximum transformation block is 32×32, the coding unit maybe partitioned into two 32×32 blocks for the transformation. In thiscase, the partitioning of the coding unit for transformation is notsignaled separately, and may be determined through comparison betweenthe horizontal or vertical size of the coding unit and the horizontal orvertical size of the maximum transformation block. For example, when thehorizontal size (width) of the coding unit is larger than the horizontalsize (width) of the maximum transformation block, the coding unit may bevertically bisected. For example, when the vertical size (length) of thecoding unit is larger than the vertical size (length) of the maximumtransformation block, the coding unit may be horizontally bisected.

Information of the maximum and/or minimum size of the coding unit andinformation of the maximum and/or minimum size of the transformationblock may be signaled or determined at an upper level of the codingunit. The upper level may be, for example, a sequence level, a picturelevel, a slice level, a tile group level, a tile level, or the like. Forexample, the minimum size of the coding unit may be determined to be4×4. For example, the maximum size of the transformation block may bedetermined to be 64×64. For example, the minimum size of thetransformation block may be determined to be 4×4.

Information of the minimum size (quad tree minimum size) of a codingunit corresponding to a leaf node of a quad tree and/or information ofthe maximum depth (the maximum tree depth of a multi-type tree) from aroot node to a leaf node of the multi-type tree may be signaled ordetermined at an upper level of the coding unit. For example, the upperlevel may be a sequence level, a picture level, a slice level, a tilegroup level, a tile level, or the like. Information of the minimum sizeof a quad tree and/or information of the maximum depth of a multi-typetree may be signaled or determined for each of an intra-picture sliceand an inter-picture slice.

Difference information between the size of a CTU and the maximum size ofa transformation block may be signaled or determined at an upper levelof the coding unit. For example, the upper level may be a sequencelevel, a picture level, a slice level, a tile group level, a tile level,or the like. Information of the maximum size of the coding unitscorresponding to the respective nodes of a binary tree (hereinafter,referred to as a maximum size of a binary tree) may be determined basedon the size of the coding tree unit and the difference information. Themaximum size of the coding units corresponding to the respective nodesof a ternary tree (hereinafter, referred to as a maximum size of aternary tree) may vary depending on the type of slice. For example, foran intra-picture slice, the maximum size of a ternary tree may be 32×32.For example, for an inter-picture slice, the maximum size of a ternarytree may be 128×128. For example, the minimum size of the coding unitscorresponding to the respective nodes of a binary tree (hereinafter,referred to as a minimum size of a binary tree) and/or the minimum sizeof the coding units corresponding to the respective nodes of a ternarytree (hereinafter, referred to as a minimum size of a ternary tree) maybe set as the minimum size of a coding block.

As another example, the maximum size of a binary tree and/or the maximumsize of a ternary tree may be signaled or determined at the slice level.Alternatively, the minimum size of the binary tree and/or the minimumsize of the ternary tree may be signaled or determined at the slicelevel.

Depending on size and depth information of the above-described variousblocks, quad partition information, multi-type tree partition indicationinformation, partition tree information and/or partition directioninformation may be included or may not be included in a bit stream.

For example, when the size of the coding unit is not larger than theminimum size of a quad tree, the coding unit does not contain quadpartition information. Thus, the quad partition information may bededuced from a second value.

For example, when the sizes (horizontal and vertical sizes) of a codingunit corresponding to a node of a multi-type tree are larger than themaximum sizes (horizontal and vertical sizes) of a binary tree and/orthe maximum sizes (horizontal and vertical sizes) of a ternary tree, thecoding unit may not be binary-partitioned or ternary-partitioned.Accordingly, the multi-type tree partition indication information maynot be signaled but may be deduced from a second value.

Alternatively, when the sizes (horizontal and vertical sizes) of acoding unit corresponding to a node of a multi-type tree are the same asthe maximum sizes (horizontal and vertical sizes) of a binary treeand/or are two times as large as the maximum sizes (horizontal andvertical sizes) of a ternary tree, the coding unit may not be furtherbinary-partitioned or ternary-partitioned. Accordingly, the multi-typetree partition indication information may not be signaled but be derivedfrom a second value. This is because when a coding unit is partitionedby a binary tree partition structure and/or a ternary tree partitionstructure, a coding unit smaller than the minimum size of a binary treeand/or the minimum size of a ternary tree is generated.

Alternatively, the binary tree partitioning or the ternary treepartitioning may be limited on the basis of the size of a virtualpipeline data unit (hereinafter, a pipeline buffer size). For example,when the coding unit is divided into sub-coding units which do not fitthe pipeline buffer size by the binary tree partitioning or the ternarytree partitioning, the corresponding binary tree partitioning or ternarytree partitioning may be limited. The pipeline buffer size may be thesize of the maximum transform block (e.g., 64×64). For example, when thepipeline buffer size is 64X64, the division below may be limited.

N×M (N and/or M is 128) Ternary tree partitioning for coding units

128×N (N<=64) Binary tree partitioning in horizontal direction forcoding units

N×128 (N<=64) Binary tree partitioning in vertical direction for codingunits

Alternatively, when the depth of a coding unit corresponding to a nodeof a multi-type tree is equal to the maximum depth of the multi-typetree, the coding unit may not be further binary-partitioned and/orternary-partitioned. Accordingly, the multi-type tree partitionindication information may not be signaled but may be deduced from asecond value.

Alternatively, only when at least one of vertical direction binary treepartitioning, horizontal direction binary tree partitioning, verticaldirection ternary tree partitioning, and horizontal direction ternarytree partitioning is possible for a coding unit corresponding to a nodeof a multi-type tree, the multi-type tree partition indicationinformation may be signaled. Otherwise, the coding unit may not bebinary-partitioned and/or ternary-partitioned. Accordingly, themulti-type tree partition indication information may not be signaled butmay be deduced from a second value.

Alternatively, only when both of the vertical direction binary treepartitioning and the horizontal direction binary tree partitioning orboth of the vertical direction ternary tree partitioning and thehorizontal direction ternary tree partitioning are possible for a codingunit corresponding to a node of a multi-type tree, the partitiondirection information may be signaled. Otherwise, the partitiondirection information may not be signaled but may be derived from avalue indicating possible partitioning directions.

Alternatively, only when both of the vertical direction binary treepartitioning and the vertical direction ternary tree partitioning orboth of the horizontal direction binary tree partitioning and thehorizontal direction ternary tree partitioning are possible for a codingtree corresponding to a node of a multi-type tree, the partition treeinformation may be signaled. Otherwise, the partition tree informationmay not be signaled but be deduced from a value indicating a possiblepartitioning tree structure.

FIG. 4 is a view showing an intra-prediction process.

Arrows from center to outside in FIG. 4 may represent predictiondirections of intra prediction modes.

Intra encoding and/or decoding may be performed by using a referencesample of a neighbor block of the current block. A neighbor block may bea reconstructed neighbor block. For example, intra encoding and/ordecoding may be performed by using an encoding parameter or a value of areference sample included in a reconstructed neighbor block.

A prediction block may mean a block generated by performing intraprediction. A prediction block may correspond to at least one among CU,PU and TU. A unit of a prediction block may have a size of one among CU,PU and TU. A prediction block may be a square block having a size of2×2, 4×4, 16×16, 32×32 or 64×64 etc. or may be a rectangular blockhaving a size of 2×8, 4×8, 2×16, 4×16 and 8×16 etc.

Intra prediction may be performed according to intra prediction mode forthe current block. The number of intra prediction modes which thecurrent block may have may be a fixed value and may be a valuedetermined differently according to an attribute of a prediction block.For example, an attribute of a prediction block may comprise a size of aprediction block and a shape of a prediction block, etc.

The number of intra-prediction modes may be fixed to N regardless of ablock size. Or, the number of intra prediction modes may be 3, 5, 9, 17,34, 35, 36, 65, or 67 etc. Alternatively, the number of intra-predictionmodes may vary according to a block size or a color component type orboth. For example, the number of intra prediction modes may varyaccording to whether the color component is a luma signal or a chromasignal. For example, as a block size becomes large, a number ofintra-prediction modes may increase. Alternatively, a number ofintra-prediction modes of a luma component block may be larger than anumber of intra-prediction modes of a chroma component block.

An intra-prediction mode may be a non-angular mode or an angular mode.The non-angular mode may be a DC mode or a planar mode, and the angularmode may be a prediction mode having a specific direction or angle. Theintra-prediction mode may be expressed by at least one of a mode number,a mode value, a mode numeral, a mode angle, and mode direction. A numberof intra-prediction modes may be M, which is larger than 1, includingthe non-angular and the angular mode. In order to intra-predict acurrent block, a step of determining whether or not samples included ina reconstructed neighbor block may be used as reference samples of thecurrent block may be performed. When a sample that is not usable as areference sample of the current block is present, a value obtained byduplicating or performing interpolation on at least one sample valueamong samples included in the reconstructed neighbor block or both maybe used to replace with a non-usable sample value of a sample, thus thereplaced sample value is used as a reference sample of the currentblock.

FIG. 7 is a diagram illustrating reference samples capable of being usedfor intra prediction.

As shown in FIG. 7, at least one of the reference sample line 0 to thereference sample line 3 may be used for intra prediction of the currentblock. In FIG. 7, the samples of a segment A and a segment F may bepadded with the samples closest to a segment B and a segment E,respectively, instead of retrieving from the reconstructed neighboringblock. Index information indicating the reference sample line to be usedfor intra prediction of the current block may be signaled. When theupper boundary of the current block is the boundary of the CTU, only thereference sample line 0 may be available. Therefore, in this case, theindex information may not be signaled. When a reference sample lineother than the reference sample line 0 is used, filtering for aprediction block, which will be described later, may not be performed.

When intra-predicting, a filter may be applied to at least one of areference sample and a prediction sample based on an intra-predictionmode and a current block size.

In case of a planar mode, when generating a prediction block of acurrent block, according to a position of a prediction target samplewithin a prediction block, a sample value of the prediction targetsample may be generated by using a weighted sum of an upper and leftside reference sample of a current sample, and a right upper side andleft lower side reference sample of the current block. In addition, incase of a DC mode, when generating a prediction block of a currentblock, an average value of upper side and left side reference samples ofthe current block may be used. In addition, in case of an angular mode,a prediction block may be generated by using an upper side, a left side,a right upper side, and/or a left lower side reference sample of thecurrent block. In order to generate a prediction sample value,interpolation of a real number unit may be performed.

In the case of intra prediction between color components, a predictionblock for the current block of the second color component may begenerated on the basis of the corresponding reconstructed block of thefirst color component. For example, the first color component may be aluma component, and the second color component may be a chromacomponent. For intra prediction between color components, the parametersof the linear model between the first color component and the secondcolor component may be derived on the basis of the template. Thetemplate may include upper and/or left neighboring samples of thecurrent block and upper and/or left neighboring samples of thereconstructed block of the first color component corresponding thereto.For example, the parameters of the linear model may be derived using asample value of a first color component having a maximum value amongsamples in a template and a sample value of a second color componentcorresponding thereto, and a sample value of a first color componenthaving a minimum value among samples in the template and a sample valueof a second color component corresponding thereto. When the parametersof the linear model are derived, a corresponding reconstructed block maybe applied to the linear model to generate a prediction block for thecurrent block. According to a video format, subsampling may be performedon the neighboring samples of the reconstructed block of the first colorcomponent and the corresponding reconstructed block. For example, whenone sample of the second color component corresponds to four samples ofthe first color component, four samples of the first color component maybe sub-sampled to compute one corresponding sample. In this case, theparameter derivation of the linear model and intra prediction betweencolor components may be performed on the basis of the correspondingsub-sampled samples. Whether or not to perform intra prediction betweencolor components and/or the range of the template may be signaled as theintra prediction mode.

The current block may be partitioned into two or four sub-blocks in thehorizontal or vertical direction. The partitioned sub-blocks may besequentially reconstructed. That is, the intra prediction may beperformed on the sub-block to generate the sub-prediction block. Inaddition, dequantization and/or inverse transform may be performed onthe sub-blocks to generate sub-residual blocks. A reconstructedsub-block may be generated by adding the sub-prediction block to thesub-residual block. The reconstructed sub-block may be used as areference sample for intra prediction of the sub-sub-blocks. Thesub-block may be a block including a predetermined number (for example,16) or more samples. Accordingly, for example, when the current block isan 8×4 block or a 4×8 block, the current block may be partitioned intotwo sub-blocks. Also, when the current block is a 4×4 block, the currentblock may not be partitioned into sub-blocks. When the current block hasother sizes, the current block may be partitioned into four sub-blocks.Information on whether or not to perform the intra prediction based onthe sub-blocks and/or the partitioning direction (horizontal orvertical) may be signaled. The intra prediction based on the sub-blocksmay be limited to be performed only when reference sample line 0 isused. When the intra prediction based on the sub-block is performed,filtering for the prediction block, which will be described later, maynot be performed.

The final prediction block may be generated by performing filtering onthe prediction block that is intra-predicted. The filtering may beperformed by applying predetermined weights to the filtering targetsample, the left reference sample, the upper reference sample, and/orthe upper left reference sample. The weight and/or the reference sample(range, position, etc.) used for the filtering may be determined on thebasis of at least one of a block size, an intra prediction mode, and aposition of the filtering target sample in the prediction block. Thefiltering may be performed only in the case of a predetermined intraprediction mode (e.g., DC, planar, vertical, horizontal, diagonal,and/or adjacent diagonal modes). The adjacent diagonal mode may be amode in which k is added to or subtracted from the diagonal mode. Forexample, k may be a positive integer of 8 or less.

An intra-prediction mode of a current block may be entropyencoded/decoded by predicting an intra-prediction mode of a blockpresent adjacent to the current block. When intra-prediction modes ofthe current block and the neighbor block are identical, information thatthe intra-prediction modes of the current block and the neighbor blockare identical may be signaled by using predetermined flag information.In addition, indicator information of an intra-prediction mode that isidentical to the intra-prediction mode of the current block amongintra-prediction modes of a plurality of neighbor blocks may besignaled. When intra-prediction modes of the current block and theneighbor block are different, intra-prediction mode information of thecurrent block may be entropy encoded/decoded by performing entropyencoding/decoding based on the intra-prediction mode of the neighborblock.

FIG. 5 is a diagram illustrating an embodiment of an inter-pictureprediction process.

In FIG. 5, a rectangle may represent a picture. In FIG. 5, an arrowrepresents a prediction direction. Pictures may be categorized intointra pictures (I pictures), predictive pictures (P pictures), andBi-predictive pictures (B pictures) according to the encoding typethereof.

The I picture may be encoded through intra-prediction without requiringinter-picture prediction. The P picture may be encoded throughinter-picture prediction by using a reference picture that is present inone direction (i.e., forward direction or backward direction) withrespect to a current block. The B picture may be encoded throughinter-picture prediction by using reference pictures that are preset intwo directions (i.e., forward direction and backward direction) withrespect to a current block. When the inter-picture prediction is used,the encoder may perform inter-picture prediction or motion compensationand the decoder may perform the corresponding motion compensation.

Hereinbelow, an embodiment of the inter-picture prediction will bedescribed in detail.

The inter-picture prediction or motion compensation may be performedusing a reference picture and motion information.

Motion information of a current block may be derived duringinter-picture prediction by each of the encoding apparatus 100 and thedecoding apparatus 200. The motion information of the current block maybe derived by using motion information of a reconstructed neighboringblock, motion information of a collocated block (also referred to as acol block or a co-located block), and/or a block adjacent to theco-located block. The co-located block may mean a block that is locatedspatially at the same position as the current block, within a previouslyreconstructed collocated picture (also referred to as a col picture or aco-located picture). The co-located picture may be one picture among oneor more reference pictures included in a reference picture list.

The derivation method of the motion information may be differentdepending on the prediction mode of the current block. For example, aprediction mode applied for inter prediction includes an AMVP mode, amerge mode, a skip mode, a merge mode with a motion vector difference, asubblock merge mode, a triangle partition mode, an inter-intracombination prediction mode, affine mode, and the like. Herein, themerge mode may be referred to as a motion merge mode.

For example, when the AMVP is used as the prediction mode, at least oneof motion vectors of the reconstructed neighboring blocks, motionvectors of the co-located blocks, motion vectors of blocks adjacent tothe co-located blocks, and a (0, 0) motion vector may be determined asmotion vector candidates for the current block, and a motion vectorcandidate list is generated by using the emotion vector candidates. Themotion vector candidate of the current block can be derived by using thegenerated motion vector candidate list. The motion information of thecurrent block may be determined based on the derived motion vectorcandidate. The motion vectors of the collocated blocks or the motionvectors of the blocks adjacent to the collocated blocks may be referredto as temporal motion vector candidates, and the motion vectors of thereconstructed neighboring blocks may be referred to as spatial motionvector candidates.

The encoding apparatus 100 may calculate a motion vector difference(MVD) between the motion vector of the current block and the motionvector candidate and may perform entropy encoding on the motion vectordifference (MVD). In addition, the encoding apparatus 100 may performentropy encoding on a motion vector candidate index and generate abitstream. The motion vector candidate index may indicate an optimummotion vector candidate among the motion vector candidates included inthe motion vector candidate list. The decoding apparatus may performentropy decoding on the motion vector candidate index included in thebitstream and may select a motion vector candidate of a decoding targetblock from among the motion vector candidates included in the motionvector candidate list by using the entropy-decoded motion vectorcandidate index. In addition, the decoding apparatus 200 may add theentropy-decoded MVD and the motion vector candidate extracted throughthe entropy decoding, thereby deriving the motion vector of the decodingtarget block.

Meanwhile, the coding apparatus 100 may perform entropy-coding onresolution information of the calculated MVD. The decoding apparatus 200may adjust the resolution of the entropy-decoded MVD using the MVDresolution information.

Meanwhile, the coding apparatus 100 calculates a motion vectordifference (MVD) between a motion vector and a motion vector candidatein the current block on the basis of an affine model, and performsentropy-coding on the MVD. The decoding apparatus 200 derives a motionvector on a per sub-block basis by deriving an affine control motionvector of a decoding target block through the sum of the entropy-decodedMVD and an affine control motion vector candidate.

The bitstream may include a reference picture index indicating areference picture. The reference picture index may be entropy-encoded bythe encoding apparatus 100 and then signaled as a bitstream to thedecoding apparatus 200. The decoding apparatus 200 may generate aprediction block of the decoding target block based on the derivedmotion vector and the reference picture index information.

Another example of the method of deriving the motion information of thecurrent may be the merge mode. The merge mode may mean a method ofmerging motion of a plurality of blocks. The merge mode may mean a modeof deriving the motion information of the current block from the motioninformation of the neighboring blocks. When the merge mode is applied,the merge candidate list may be generated using the motion informationof the reconstructed neighboring blocks and/or the motion information ofthe collocated blocks. The motion information may include at least oneof a motion vector, a reference picture index, and an inter-pictureprediction indicator. The prediction indicator may indicateone-direction prediction (L0 prediction or L1 prediction) ortwo-direction predictions (L0 prediction and L1 prediction).

The merge candidate list may be a list of motion information stored. Themotion information included in the merge candidate list may be at leastone of motion information (spatial merge candidate) of a neighboringblock adjacent to the current block, motion information (temporal mergecandidate) of the collocated block of the current block in the referencepicture, new motion information generated by a combination of the motioninformation exiting in the merge candidate list, motion information(history-based merge candidate) of the block that is encoded/decodedbefore the current block, and zero merge candidate.

The encoding apparatus 100 may generate a bitstream by performingentropy encoding on at least one of a merge flag and a merge index andmay signal the bitstream to the decoding apparatus 200. The merge flagmay be information indicating whether or not to perform the merge modefor each block, and the merge index may be information indicating thatwhich neighboring block, among the neighboring blocks of the currentblock, is a merge target block. For example, the neighboring blocks ofthe current block may include a left neighboring block on the left sideof the current block, an upper neighboring block disposed above thecurrent block, and a temporal neighboring block temporally adjacent tothe current block.

Meanwhile, the coding apparatus 100 performs entropy-coding on thecorrection information for correcting the motion vector among the motioninformation of the merge candidate and signals the same to the decodingapparatus 200. The decoding apparatus 200 can correct the motion vectorof the merge candidate selected by the merge index on the basis of thecorrection information. Here, the correction information may include atleast one of information on whether or not to perform the correction,correction direction information, and correction size information. Asdescribed above, the prediction mode that corrects the motion vector ofthe merge candidate on the basis of the signaled correction informationmay be referred to as a merge mode having the motion vector difference.

The skip mode may be a mode in which the motion information of theneighboring block is applied to the current block as it is. When theskip mode is applied, the encoding apparatus 100 may perform entropyencoding on information of the fact that the motion information of whichblock is to be used as the motion information of the current block togenerate a bit stream, and may signal the bitstream to the decodingapparatus 200. The encoding apparatus 100 may not signal a syntaxelement regarding at least any one of the motion vector differenceinformation, the encoding block flag, and the transform coefficientlevel to the decoding apparatus 200.

The subblock merge mode may mean a mode that derives the motioninformation in units of sub-blocks of a coding block (CU). When thesubblock merge mode is applied, a subblock merge candidate list may begenerated using motion information (sub-block based temporal mergecandidate) of the sub-block collocated to the current sub-block in thereference image and/or an affine control point motion vector mergecandidate.

The triangle partition mode may mean a mode that derives motioninformation by partitioning the current block into diagonal directions,derives each prediction sample using each of the derived motioninformation, and derives the prediction sample of the current block byweighting each of the derived prediction samples.

The inter-intra combined prediction mode may mean a mode that derives aprediction sample of the current block by weighting a prediction samplegenerated by inter prediction and a prediction sample generated by intraprediction.

The decoding apparatus 200 may correct the derived motion information byitself. The decoding apparatus 200 may search the predetermined regionon the basis of the reference block indicated by the derived motioninformation and derive the motion information having the minimum SAD asthe corrected motion information.

The decoding apparatus 200 may compensate a prediction sample derivedvia inter prediction using an optical flow.

FIG. 6 is a diagram illustrating a transform and quantization process.

As illustrated in FIG. 6, a transform and/or quantization process isperformed on a residual signal to generate a quantized level signal. Theresidual signal is a difference between an original block and aprediction block (i.e., an intra prediction block or an inter predictionblock). The prediction block is a block generated through intraprediction or inter prediction. The transform may be a primarytransform, a secondary transform, or both. The primary transform of theresidual signal results in transform coefficients, and the secondarytransform of the transform coefficients results in secondary transformcoefficients.

At least one scheme selected from among various transform schemes whichare preliminarily defined is used to perform the primary transform. Forexample, examples of the predefined transform schemes include discretecosine transform (DCT), discrete sine transform (DST), andKarhunen-Loeve transform (KLT). The transform coefficients generatedthrough the primary transform may undergo the secondary transform. Thetransform schemes used for the primary transform and/or the secondarytransform may be determined according to coding parameters of thecurrent block and/or neighboring blocks of the current block.Alternatively, transform information indicating the transform scheme maybe signaled. The DCT-based transform may include, for example, DCT-2,DCT-8, and the like. The DST-based transform may include, for example,DST-7.

A quantized-level signal (quantization coefficients) may be generated byperforming quantization on the residual signal or a result of performingthe primary transform and/or the secondary transform. The quantizedlevel signal may be scanned according to at least one of a diagonalup-right scan, a vertical scan, and a horizontal scan, depending on anintra prediction mode of a block or a block size/shape. For example, asthe coefficients are scanned in a diagonal up-right scan, thecoefficients in a block form change into a one-dimensional vector form.Aside from the diagonal up-right scan, the horizontal scan ofhorizontally scanning a two-dimensional block form of coefficients orthe vertical scan of vertically scanning a two-dimensional block form ofcoefficients may be used depending on the intra prediction mode and/orthe size of a transform block. The scanned quantized-level coefficientsmay be entropy-encoded to be inserted into a bitstream.

A decoder entropy-decodes the bitstream to obtain the quantized-levelcoefficients. The quantized-level coefficients may be arranged in atwo-dimensional block form through inverse scanning. For the inversescanning, at least one of a diagonal up-right scan, a vertical scan, anda horizontal scan may be used.

The quantized-level coefficients may then be dequantized, then besecondary-inverse-transformed as necessary, and finally beprimary-inverse-transformed as necessary to generate a reconstructedresidual signal.

Inverse mapping in a dynamic range may be performed for a luma componentreconstructed through intra prediction or inter prediction beforein-loop filtering. The dynamic range may be divided into 16 equal piecesand the mapping function for each piece may be signaled. The mappingfunction may be signaled at a slice level or a tile group level. Aninverse mapping function for performing the inverse mapping may bederived on the basis of the mapping function. In-loop filtering,reference picture storage, and motion compensation are performed in aninverse mapped region, and a prediction block generated through interprediction is converted into a mapped region via mapping using themapping function, and then used for generating the reconstructed block.However, since the intra prediction is performed in the mapped region,the prediction block generated via the intra prediction may be used forgenerating the reconstructed block without mapping/inverse mapping.

When the current block is a residual block of a chroma component, theresidual block may be converted into an inverse mapped region byperforming scaling on the chroma component of the mapped region. Theavailability of the scaling may be signaled at the slice level or thetile group level. The scaling may be applied only when the mapping forthe luma component is available and the division of the luma componentand the division of the chroma component follow the same tree structure.The scaling may be performed on the basis of an average of sample valuesof a luma prediction block corresponding to the color difference block.In this case, when the current block uses inter prediction, the lumaprediction block may mean a mapped luma prediction block. A valuenecessary for the scaling may be derived by referring to a lookup tableusing an index of a piece to which an average of sample values of a lumaprediction block belongs. Finally, by scaling the residual block usingthe derived value, the residual block may be switched to the inversemapped region. Then, chroma component block restoration, intraprediction, inter prediction, in-loop filtering, and reference picturestorage may be performed in the inverse mapped area.

Information indicating whether the mapping/inverse mapping of the lumacomponent and chroma component is available may be signaled through aset of sequence parameters.

The prediction block of the current block may be generated on the basisof a block vector indicating a displacement between the current blockand the reference block in the current picture. In this way, aprediction mode for generating a prediction block with reference to thecurrent picture is referred to as an intra block copy (IBC) mode. TheIBC mode may be applied to M×N (M<=64, N<=64) coding units. The IBC modemay include a skip mode, a merge mode, an AMVP mode, and the like. Inthe case of a skip mode or a merge mode, a merge candidate list isconstructed, and the merge index is signaled so that one merge candidatemay be specified. The block vector of the specified merge candidate maybe used as a block vector of the current block. The merge candidate listmay include at least one of a spatial candidate, a history-basedcandidate, a candidate based on an average of two candidates, and azero-merge candidate. In the case of an AMVP mode, the difference blockvector may be signaled. In addition, the prediction block vector may bederived from the left neighboring block and the upper neighboring blockof the current block. The index on which neighboring block to use may besignaled. The prediction block in the IBC mode is included in thecurrent CTU or the left CTU and limited to a block in the alreadyreconstructed area. For example, a value of the block vector may belimited such that the prediction block of the current block ispositioned in an area of three 64×64 blocks preceding the 64×64 block towhich the current block belongs in the coding/decoding order. Bylimiting the value of the block vector in this way, memory consumptionand device complexity according to the IBC mode implementation may bereduced.

Hereinafter, a transform coefficient encoding/decoding method accordingto an embodiment of the present invention will be described. In theembodiment below, a current block may be a transform unit or a transformblock.

In the present invention, the transform coefficient for the currentblock may mean a coefficient derived as a result of transforming aresidual signal for the current block, or a quantized level value of thetransform coefficient.

FIG. 8 is a diagram illustrating a transform coefficientencoding/decoding method according to an embodiment of the presentinvention.

Referring to FIG. 8, the transform coefficient encoding/decoding methodmay include: [D1] a step of grouping transform coefficients; [D2] a stepof scanning the transform coefficients; and [D3] a step of binarizingthe transform coefficients.

[D1] A Transform Coefficient Grouping Step

In encoding/decoding of the transform coefficient for the current block,the transform coefficient grouping may be performed using at least onemethod among fixed block transform coefficient grouping and variableblock transform coefficient grouping.

The encoding/decoding of the transform coefficient for the current blockmay be performed on a per-transform coefficient group basis.

K transform coefficient groups may be independently subjected totransform coefficient encoding/decoding. Further, the K transformcoefficient groups may be independently subjected to predictionencoding/decoding, and may be independently subjected to transform andquantization. Herein, K may be a positive integer.

In the meantime, the transform coefficient group may be defined as atransform coefficient block, a child transform block, or a sub transformblock.

Transform coefficient grouping for the current block according to theembodiment of the present invention may be performed as the fixed blocktransform coefficient grouping.

Specifically, the transform coefficients for the current block may bedivided into transform coefficient groups, each in a fixed M (width)×N(height) size.

FIGS. 9 to 12 are diagrams illustrating an example of fixed blocktransform coefficient grouping of the present invention.

FIG. 9 shows an example in which transform coefficient grouping isperformed with a size that is the same as the size of the current block.Referring to FIG. 9, when the current block is in an 8×8 size, the sizeof the transform coefficient group is set to 8×8 and the current blockmay be a transform coefficient group.

FIG. 10 shows an example in which the current block is partitioned witha predetermined size and is subjected to transform coefficient grouping.Referring to FIG. 10, when the current block is in a 16×16 size and thetransform coefficient group is in a predetermined size, which is a 4×4size, the current block is divided into 16 transform coefficient groupsfor grouping.

FIG. 11 shows an example of transform coefficient grouping when thecurrent block is not exactly divided by the transform coefficient groupin size. Referring to FIG. 11, when the current block is in a 16×16 sizeand the transform coefficient group is in a predetermined size, which isa 5×5 size, transform coefficient groups in subblock sizes, such as 5×1,1×5, and 1×1, are allowed with respect to the right and bottomboundaries of the current block.

FIG. 12 shows an example of transform coefficient grouping when thehorizontal or vertical size of a predetermined transform coefficientgroup is larger than the horizontal or vertical size of the currentblock. Referring to FIG. 12, when the current block is in a 16×4 sizeand the predetermined transform coefficient group is in an 8×8 size, an8×4-sized transform coefficient group is allowed. That is, the size ofthe predetermined transform coefficient group may vary in accordancewith the size of the current block.

In the meantime, when the current block is present at the right or lowerboundary of the picture or when the current block is not exactly dividedby the transform coefficient group in size, a transform coefficientgroup which is in a size different from a fixed transform coefficientgroup size is allowed, as described above with reference to FIGS. 11 and12.

Transform coefficient grouping for the current block according to theembodiment of the present invention may be performed as variable blocktransform coefficient grouping.

Specifically, the transform coefficients for the current block may bedivided into k transform coefficient groups in different sizes. Invariable block transform coefficient grouping, the current block may bepartitioned into k transform coefficient groups that have the positionand the size of the transform coefficient group having the optimum cost.In the meantime, the k transform coefficient groups resulting from thevariable block transform coefficient grouping may not overlap eachother.

FIGS. 13 to 15 are diagrams illustrating an example of variable blocktransform coefficient grouping of the present invention.

As shown in FIG. 13, when the current block is in a 16×16 size, thecurrent block is divided in such a manner that the transform coefficientgroup at the top left position is in an 8×8 size and the remainingtransform coefficient groups are in a 4×4 size.

As shown in FIG. 14, when the current block is in a 16×16 size, thecurrent block is divided in such a manner that the transform coefficientgroup at the left position is in a 4×8 size and the remaining transformcoefficient groups are in a 4×4 size. Alternatively, when the currentblock is in a 16×16 size, the current block is divided in such a mannerthat the transform coefficient group at the top position is in an 8×4size and the remaining transform coefficient groups are in a 4×4 size.

As shown in FIG. 15, when the current block is in a 16×16 size, thecurrent block is divided in such a manner that the transform coefficientgroup at the top left position is in an 8×8 size, the transformcoefficient group at the left position is in a 4×8 size, the transformcoefficient group at the top position is in an 8×4 size, and theremaining transform coefficient groups are in a 4×4 size.

In the meantime, the transform coefficient grouping method for thecurrent block may be indexed into a grouping method having the optimumcost among N grouping methods, wherein N is any positive integer.

For example, an index list of five grouping methods may be constructedas follows, and index information indicating a method having the minimumRD-cost may be signaled.

index 0: a fixed block transform coefficient grouping method;

index 1: a first variable block transform coefficient grouping method;

index 2: a second variable block transform coefficient grouping method;

index 3: a third variable block transform coefficient grouping method;

index 4: a fourth variable block transform coefficient grouping method;

In performing transform coefficient grouping, the transform coefficientgrouping method may be determined on the basis of an encoding parameter,for example, at least one among the slice type, the tile group type, theencoding mode, the intra prediction mode, the inter prediction mode, thevalue of the transform coefficient, and the size/shape of the currentblock. The transform coefficient grouping method may be at least oneamong the fixed block transform coefficient grouping method and thevariable block transform coefficient grouping method described above.

On the basis of the slice type, the transform coefficient groupingmethod may be determined.

For example, when the current slice is slice I, the variable blocktransform coefficient grouping method is determined. When the currentslice is slice P or slice B, the fixed block transform coefficientgrouping method is determined.

On the basis of the position of the non-zero transform coefficientwithin the current block, the transform coefficient grouping method maybe determined.

For example, one transform coefficient group in the minimum size whichincludes all the non-zero transform coefficients within the currentblock may be determined. Herein, the transform coefficient group may bein a size of (X_max+1)×(Y_max+1), wherein X_max is the maximum value forthe X-coordinate positions of the non-zero transform coefficients withinthe current block and Y_max is the maximum value for the Y-coordinatepositions of the non-zero transform coefficients within the currentblock.

FIG. 16 is a diagram illustrating a method of determining a transformcoefficient group on the basis of a position of a non-zero transformcoefficient within a current block.

Referring to FIG. 16, in a 16×16-sized coding block, one transformcoefficient group 0 in the minimum size (6×6) which includes all thenon-zero transform coefficients may be determined.

The example of determining the transform coefficient grouping method onthe basis of the position of the non-zero coefficient within the currentblock may be performed only, in a case where the current block is in anN×M size, when min(N, M) or max(N, M) is larger than a threshold valueK, which is any positive integer.

On the basis of the prediction mode, the transform coefficient groupingmethod may be determined.

For example, when the current block is in the intra prediction mode, thevariable block transform coefficient grouping method is determined. Whenthe current block is in the inter prediction mode, the fixed blocktransform coefficient grouping method is determined.

On the basis of the intra prediction mode, the transform coefficientgrouping method may be determined.

For example, when the intra prediction mode of the current block is theDC/Planar mode, it is determined that the variable block transformcoefficient grouping method described with reference to FIG. 13 is used.When the intra prediction mode of the current block is a horizontalangular mode, it is determined that the variable block transformcoefficient grouping method described with reference to FIG. 14 is used.When the intra prediction mode of the current block is a verticalangular mode, it is determined that the transform coefficient groupingmethod described with reference to FIG. 15 is used.

On the basis of the size of the current block, the transform coefficientgrouping method may be determined.

For example, when the minimum value (min(N, M)) or the maximum value(max (N, M)) of the width (M) and the height (N) of the current block(M×N) is larger than the threshold value K, which is any positiveinteger, the variable block transform coefficient grouping method isdetermined. Otherwise, the fixed block transform coefficient groupingmethod is determined.

For example, when the width (M) and the height (N) of the current block(M×N) are the same, the fixed block transform coefficient groupingmethod is determined. When the width (M) and the height (N) of thecurrent block (M×N) differ, the variable block transform coefficientgrouping method is determined.

For example, when the width (M) of the current block (M×N) is smallerthan the height (N) and is also smaller than a predefined value (P), thewidth of the transform coefficient group is fixed to the width (M) ofthe current block and then transform coefficient grouping is performed.Herein, P may be a positive integer, for example, 4.

For example, when the height (N) of the current block (M×N) is smallerthan the width (M) and is also smaller than a predefined value (Q), theheight of the transform coefficient group is fixed to the height (N) ofthe current block and then transform coefficient grouping is performed.Herein, Q may be a positive integer, for example, 4.

FIGS. 17 to 20 are diagrams illustrating how to determine a transformcoefficient grouping method on the basis of a width (M) or a height (N)of a current block (M×N).

For example, when the width (M) of the current block is larger than anythreshold value, transform coefficient grouping is performed withdivision of M by 4 as shown in FIG. 17.

For example, when the width (M) of the current block is larger than anythreshold value, transform coefficient grouping is performed withdivision of M by 2 as shown in FIG. 18.

For example, when the height (N) of the current block is larger than anythreshold value, transform coefficient grouping is performed withdivision of N by 4 as shown in FIG. 19.

For example, when the height (N) of the current block is larger than anythreshold value, transform coefficient grouping is performed withdivision of N by 2 as shown in FIG. 20.

For example, when the width (M) or the height (N) of the current blockis smaller than any threshold value (T), transform coefficient groupingis performed into a transform coefficient group in a B×B size.Conversely, when the width (M) and the height (N) of the current blockare equal to or larger than the any threshold value, transformcoefficient grouping is performed into a transform coefficient group ina 2B×2B size. Herein, T may be a positive integer, for example, 4, and Bmay be a positive integer, for example, 2.

For example, when the area of the current block (M×N) is larger than anythreshold value (R) and is in a non-square shape, transform coefficientgrouping is performed into a transform coefficient group in a non-squareshape. Herein, R may be a positive integer, for example, 8.

The area of the transform coefficient group may be fixed into at leastone unit among a sub-CU, a CU, a CTU, a tile, a tile group, a brick, aslice, a picture, and a sequence. Herein, the area of the transformcoefficient group may be the product of the width and the height of thetransform coefficient group, and may be a positive integer.

For example, the area of the transform coefficient group may have avalue of {4, 8, 16, 32, 64, 128, 256, 512}. Herein, the area of thetransform coefficient group may be transmitted on the basis of at leastone among a sub-CU, a CU, a CTU, a tile, a tile group, a brick, a slice,a picture, and a sequence.

For example, a value obtained by applying log 2 to the area of thetransform coefficient group may be transmitted.

For example, a value obtained by applying log 2 to the area of thetransform coefficient group is added to −2, and the resulting value maybe transmitted.

For example, a value obtained by applying log 2 to the area of thetransform coefficient group is added to −3, and the resulting value maybe transmitted.

The transform coefficient group may be partitioned into sub transformcoefficient groups.

For example, transform and quantization may be performed on a pertransform coefficient group basis, and scanning and binarization oftransform coefficients may be performed on a per sub transformcoefficient group basis.

Using the intra prediction mode and the position information of the lastnon-zero coefficient, the transform coefficient grouping method may bedetermined.

A residual signal after intra prediction may have a correlationaccording to the intra prediction direction. Therefore, there is acharacteristic that when horizontal direction prediction is used, themost non-zero coefficients after frequency transform occur in the firstcolumn; and conversely, when vertical direction prediction is used, themost non-zero coefficients after frequency transform occur in the firstrow.

Using such a characteristic and the position information of the lastnon-zero coefficient after frequency transform, transform coefficientgrouping may be effectively performed. Herein, the wording effective maymean that a much larger transform coefficient group is generated toreduce the number of coefficient presence indicators based on atransform coefficient group (block) to be signaled.

FIGS. 21 to 23 are diagrams illustrating a method of setting a transformcoefficient group by using an intra prediction mode and positioninformation of the last non-zero coefficient.

FIG. 21 shows an example where when the intra prediction mode is thehorizontal direction, transform coefficient grouping is performed usingthe position information of the last non-zero coefficient.

Referring to FIG. 21, in intra horizontal direction prediction, thefirst transform coefficient group has the vertical size, starting fromthe position (0, 0), which may be the same as the vertical size of thecurrent block; and the horizontal size of the first transformcoefficient group may be determined to be the x position+1 of the lastnon-zero transform coefficient. Herein, intra prediction horizontaldirection may include an intra prediction mode having a directionsimilar to the horizontal direction, namely, a direction at an angle ofless than +−90 degrees, with the horizontal direction in the center.

FIG. 22 shows an example where when the intra prediction mode is thevertical direction, transform coefficient grouping is performed usingposition information of the last non-zero coefficient.

Referring to FIG. 22, in intra vertical direction prediction, the firsttransform coefficient group has the horizontal size, starting from theposition (0, 0), which is the same as the horizontal size of the currentblock; and the vertical size of the first transform coefficient groupmay be determined to be the y position+1 of the last non-zero transformcoefficient. Herein, intra prediction vertical direction may include anintra prediction mode having a direction similar to the verticaldirection, namely, a direction at an angle of less than +−90 degrees,with the vertical direction in the center.

FIG. 23 shows an example where the intra prediction mode is anon-angular prediction mode, transform coefficient grouping is performedusing the position information of the last non-zero coefficient.

Referring to FIG. 23, in non-angular intra prediction, the firsttransform coefficient group may be determined to be in a minimum-sizedtriangular shape including the position of the last non-zerocoefficient. Herein, the non-angular prediction modes may include thePlanar mode and the DC mode.

In the meantime, using the transform coefficient scanning method,instead of the intra prediction mode, and the position information ofthe last non-zero coefficient, the transform coefficient grouping methodmay be determined.

In the examples described with reference to FIGS. and 22, the transformcoefficient group may be set according to the scanning method, withoutusing the intra prediction mode.

For example, in the case of using horizontal scanning, the transformcoefficient group may be set in the same manner as in FIG. 21. In thecase of using vertical scanning, the transform coefficient group may beset in the same manner as in FIG. 22. Besides, in the case of usingzigzag or diagonal scanning, the transform coefficient group may be setusing the method as in FIG. 23.

With respect to a remaining non-zero out region except for a zero outregion, transform coefficient grouping may be performed.

Specifically, the remaining region except for the zero out region may besubjected to transform coefficient grouping. That is, transformcoefficient grouping may be performed in the non-zero out region.

For example, in the non-zero out region, transform coefficient groupsincluding all the non-zero transform coefficients may be generated.

In the meantime, the zero out region/non-zero out region may bepredefined in the encoder and the decoder, or may be determined on thebasis of signaled information in a particular header (a VPS, an SPS, aPPS, a slice, a brick, a tile group, or the like).

In the meantime, in the current block, a region having a predefinedvalue (T) or larger may be set as a zero out region. Herein, T may be apositive integer, for example, 32. That is, when the width or height ofthe current block is equal to or larger than a predefined size, a regionin a predefined size or larger within the current block is determined asthe zero out region.

For example, when the current block is in a 64×64 size and thepredefined value is 32, the region other than a 32×32-sized region atthe top left of the current block is set as the zero out region.

For example, when the current block is in a 16×64 size and thepredefined value is 32, the region other than a 16×32-sized region atthe top left of the current block is set as the zero out region.

Alternatively, the zero out region/non-zero out region may be determinedon the basis of at least one among the size of the current block and thetype of frequency transform.

For example, when as the type of frequency transform, the type oftransform (for example, DST-7 or DCT-8) other than DCT-2 is used and thecurrent block (or the transform block) is in a 64×64 size, the regionexcept for the top left transform region in a 32×32 size is determinedas the zero out region.

For example, when the type of transform (for example, DST-7 or DCT-8)other than DCT-2 is used as the type of frequency transform, thenon-zero out region is set to be the M×M-sized region at the top left ofthe current block. In this case, the region other than the M×M-sizedregion at the top left may be set as the zero out region. Herein, M maybe a positive integer, for example, 16.

In the meantime, the determination of the zero out region/non-zero outregion may be performed by a combination of one or more examplesdescribed above.

FIGS. 24 and 25 are diagrams illustrating a zero out region and anon-zero out region according to an embodiment of the present invention.

FIG. 24 shows an example of a zero out region in a quadrangular shape.

FIG. 25 shows an example of a zero out region in a triangular shape.

Regarding the transform coefficient grouping for the non-zero outregion, according to the zero out region, one or more transformcoefficient groups in a fixed size may be configured, or transformcoefficient groups in different sizes that may minimally include a zeroout region may be configured.

FIGS. 26 and 27 are diagrams illustrating transform coefficient groupingin a non-zero out region.

Referring to FIG. 26, when an 8×8-sized region at the bottom rightwithin a 16×16-sized block is defined as the zero out region, groupinginto three 8×8-sized transform coefficient groups takes place.

Referring to FIG. 27, when the triangular region at the bottom rightwithin the 16×16-sized block is defined as the zero out region and it isassumed that the minimum size of the transform coefficient group is 4×4,six 4×4-sized transform coefficient groups and one 8×8-sized transformcoefficient group are configured to minimally include the zero outregion.

[D2] A Transform Coefficient Scanning Step

In performing encoding/decoding of the transform coefficient for thecurrent block, the transform coefficient scanning may be performed usingat least one among fixed transform coefficient scanning and adaptivetransform coefficient scanning. Further, the above-described scanningmethod may be performed on the transform coefficient group.

FIG. 28 is a diagram illustrating examples of a fixed transformcoefficient scanning method.

Referring to FIG. 28, the fixed transform coefficient scanning methodmay be performed by any one among diagonal scanning, horizontalscanning, vertical scanning, and zigzag scanning.

In the meantime, the fixed transform scanning method may be determinedon the basis of at least one among a current block, a tile, a tilegroup, a brick, a slice, a picture, and a sequence.

Regarding the adaptive transform coefficient scanning, the transformcoefficient scanning method may be adaptively determined on the basis ofthe encoding parameter.

For example, the transform coefficient scanning method may be determinedon the basis of at least one among the quantization parameter, thetransform method, the encoding mode, the intra prediction mode, theinter prediction mode, the value of the transform coefficient, and thesize/shape of the current block.

As another example, when the current block is in the intra predictionmode and is processed in the DC/PLANAR prediction mode, the transformcoefficient scanning method is determined to be diagonal scanning.

As still another example, when the current block is in the intraprediction mode and is processed in the horizontal angular predictionmode, the transform coefficient scanning method is determined to bevertical scanning.

As still another example, when the current block is in the intraprediction mode and is processed in the vertical angular predictionmode, the transform coefficient scanning method is determined to behorizontal scanning.

In the meantime, a transform coefficient scanning candidate list of Ncandidates may be configured on the basis of at least one among apicture, a slice, a brick, a tile group, a tile, a coding block, and atransform coefficient group, wherein N is a positive integer. In thiscase, the transform coefficient scanning candidate list may beconfigured on the basis of at least one among the encoding mode, thetransform method, the inter prediction mode, and the intra predictionmode. The encoder may encode index information indicating the scanningmethod having the optimum cost, for example, generated bits, andRD-cost, in the transform coefficient scanning candidate list. Thedecoder may select the transform coefficient scanning method from thetransform scanning coefficient candidate list by using the indexinformation.

In the meantime, the transform coefficient scanning candidate list maybe constructed on the basis of the transform coefficient scanning methodfor the neighboring block of the current block.

In the meantime, the transform coefficient scanning may be performed onthe transform coefficient and the transform coefficient group that areincluded in the non-zero out region except for the zero out region.

The syntax elements (last_significant_coeff_x_prefix/suffix,last_significant_coeff_y_prefix/suffix), which mean the start of thescanning or the position of the last non-zero transform coefficientwithin the current transform block, are intended to represent only theposition of the transform coefficient included in the non-zero outregion, so that the maximum range of the syntax elements may be limited,causing the syntax elements to be represented by much shorter bits.

For example, in the case where only a 32×32-sized region at the top leftwithin a 64×64-sized transform block is defined as the non-zero outregion, each of the positions x and y of the last transform coefficientmay have a range of 0 to 31. Therefore, when represented by fixed bits,the position is represented by 5 bits.

The encoder may scan the transform coefficient groups included in thenon-zero out region according to a predefined transform coefficientscanning method (or scanning order), and may scan the transformcoefficients within the corresponding transform coefficient groupsaccording to the predefined transform coefficient scanning method (orscanning order).

Herein, the transform coefficients may be encoded by starting thescanning from the transform coefficient that is present at the positionof the last transform coefficient included in the non-zero out region.

The decoder may decode the position of the last transform coefficientfrom the bitstream and may perform scanning on the non-zero out regionstarting from the position of the last transform coefficient accordingto the predefined transform coefficient scanning method (or scanningorder) so that the positions of the decoded transform coefficientswithin the transform coefficient block may be derived.

[D3] A Transform Coefficient Binarization Step

Binarization of the transform coefficient may be performed using atleast one method among transform coefficient presence indicatorbinarization, transform coefficient sign binarization, and transformcoefficient absolute value binarization. Herein, binarization may meanentropy encoding/decoding.

Hereinafter, the binarization of the transform coefficient presenceindicator, of the transform coefficient sign, and of the transformcoefficient absolute value will be described.

[D3-1] Binarization of a Transform Coefficient Presence Indicator

A transform coefficient presence indicator is an indicator indicatingwhether or not the non-zero transform coefficient is present.

The transform coefficient presence indicator may be encoded/decoded onthe basis of the transform coefficient or the transform coefficientgroup.

The transform coefficient presence indicator based on the transformcoefficient is set to “1” on the basis of the transform coefficient whenthe value of the transform coefficient is not 0, and is set to “0” whenthe value of the transform coefficient is 0.

The transform coefficient presence indicator based on the transformcoefficient group is set to “1” when the non-zero transform coefficientis present in the corresponding transform coefficient group, and is setto “0” when the non-zero transform coefficient is not present.

When the transform coefficient presence indicator based on the transformcoefficient group is “0”, the coefficient presence indicator based onthe transform coefficient within the transform coefficient group is notencoded/decoded. In this case, the transform coefficient presenceindicator based on the transform coefficient within the transformcoefficient group may be regarded to be “0”.

FIG. 29 is a diagram illustrating a transform coefficient presenceindicator based on a transform coefficient and a transform coefficientpresence indicator based on a transform coefficient group.

In FIG. 29, the current block is in an 8×8 size, and the transformcoefficient group is in a 4×4 size.

Referring to FIG. 29, when the transform coefficient presence indicatorbased on the transform coefficient group is “0”, the transformcoefficient presence indicator based on the transform coefficient is notencoded/decoded and thus does not present.

In the meantime, transform may not be performed in the zero out region,so that the transform coefficient presence indicator based on thetransform coefficient group and the transform coefficient presenceindicator based on the transform coefficient may be concealed withrespect to the transform coefficient groups and the transformcoefficients included in the zero out region. Herein, the concealmentmay mean that encoding/decoding is not performed or transmission fromthe encoder to the decoder does not take place.

Accordingly, the decoder may not entropy decode pieces of syntax of thetransform coefficient presence indicator based on the transformcoefficient group and the transform coefficient presence indicator basedon the transform coefficient with respect to the transform coefficientgroups and the transform coefficients that are included in the zero outregion, and the value of the transform coefficient presence indicatorbased on the transform coefficient group and the value of the transformcoefficient presence indicator based on the transform coefficient may beregarded to be “0”.

As described above, the zero out region may be predefined in the encoderand the decoder, or may be determined on the basis of signaledinformation in a particular header (a VPS, an SPS, a PPS, a slice, abrick, a tile group, or the like). Therefore, the transform coefficientpresence indicator based on the transform coefficient group and thetransform coefficient presence indicator based on the transformcoefficient may be concealed on the basis of information for determiningthe zero out region.

Further, the zero out region may be determined on the basis of at leastone among the size of the current block and the type of frequencytransform, so that the transform coefficient presence indicator based onthe transform coefficient group and the transform coefficient presenceindicator based on the transform coefficient may be concealed on thebasis of at least one among the size of the current block and the typeof frequency transform.

For example, as shown in FIG. 26, when the current block is in a 16×16size and the grey 8×8-sized region is determined as the zero out region,the encoder does not transmit at least one transform coefficientpresence indicator based on the transform coefficient group and at leastone transform coefficient presence indicator based on the transformcoefficient, with respect to the transform coefficient groups includedwithin the grey region. Further, the decoder may not entropy decode atleast one transform coefficient presence indicator based on thetransform coefficient group and at least one transform coefficientpresence indicator based on the transform coefficient with respect tothe corresponding region, and the values of the corresponding transformcoefficient presence indicators based on the transform block coefficientand the values of the corresponding transform coefficient presenceindicators based on the transform coefficient may be regarded to be “0”.

For example, as shown in FIG. 27, when the zero out region is in atriangular shape and the minimum transform coefficient group is definedto be in a 4×4 size, at least one transform coefficient presenceindicator based on the transform coefficient for the zero out regionincluded in the transform coefficient group is not transmitted by theencoder and is regarded, by the decoder, to have the value of 0. Allother transform coefficient presence indicators based on the transformcoefficient group of the zero out region and transform coefficientpresence indicators based on the transform coefficient may be concealed.

For example, when as the type of transform, the type of transform (forexample, DST7 or DCT8) other than DCT2 is used and the current block isin a 64×64 size, the region except for the top left transform region ina 32×32 size is defined as the zero out region. With respect to thetransform coefficient groups included in the corresponding region, theencoder may not transmit at least one transform coefficient presenceindicator based on the transform coefficient group and at least onetransform coefficient presence indicator based on the transformcoefficient, and the decoder may not entropy decode at least onetransform coefficient presence indicator based on the transformcoefficient group and at least one transform coefficient presenceindicator based on the transform coefficient with respect to thecorresponding region. Further, the values of the corresponding transformcoefficient presence indicators based on the transform coefficient groupand the values of the corresponding transform coefficient presenceindicators based on the transform coefficient may be regarded to be “0”.

When the transform coefficient presence indicator based on the transformcoefficient group or the transform coefficient presence indicator basedon the transform coefficient is subjected to binarization (entropyencoding/decoding), the transform coefficient groups uses differentprobability information (context) in performing entropyencoding/decoding of the transform coefficient presence indicator basedon the transform coefficient group or the transform coefficient presenceindicator based on the transform coefficient.

For example, in the case shown in FIG. 26, the top left 8×8-sized blockbased on the transform coefficient and the other blocks use differentprobability information in performing entropy encoding/decoding of atransform coefficient presence indicator based on the transformcoefficient group or a transform coefficient presence indicator based onthe transform coefficient.

For example, in the case shown in FIG. 27, the 4×4-sized transformcoefficient group including a part of the zero out region and the4×4-sized transform coefficient group not including the zero out regionuses different probability information in performing entropyencoding/decoding of the transform coefficient presence indicator basedon the transform coefficient group or the transform coefficient presenceindicator based on the transform coefficient.

Further, on the basis of the size of each transform coefficient group,different probability information may be used in performing entropyencoding/decoding of the transform coefficient presence indicator basedon the transform coefficient group or the transform coefficient presenceindicator based on the transform coefficient.

[D3-2] A Transform Coefficient Sign Binarization

In performing transform coefficient sign binarization for the currentblock, binarization of the transform coefficient sign may be performedusing at least one method among a transform coefficient sign indicator,transform coefficient sign concealment, and transform coefficient signprediction.

In binarization of the transform coefficient sign for the current block,the transform coefficient sign indicator may be used.

For example, the transform coefficient sign indicator is set to “1” whenthe transform coefficient is a negative number (−), and is set to “0”when the transform coefficient is a positive number (+). Conversely, thetransform coefficient sign indicator is set to “0” when the transformcoefficient is a negative number (−), and is set to “1” when thetransform coefficient is a positive number (+).

For example, when the transform coefficient presence indicator based onthe transform coefficient or the transform coefficient presenceindicator based on the transform coefficient group is “0”, the transformcoefficient sign indicator is not encoded/decoded.

In the meantime, in binarization of the transform coefficient sign forthe current block, transform coefficient sign concealment may be used.

The transform coefficient sign concealment may be to derive N pieces oftransform coefficient sign information according to the state of thetransform coefficient absolute value, wherein N may be a positiveinteger, and may be performed on a per transform coefficient groupbasis.

For example, when the sum of the transform coefficients of the transformcoefficient group is an even number, the first non-zero transformcoefficient has a positive sign “+”.

For example, when the sum of the transform coefficients of the transformcoefficient group is an even number, the first non-zero transformcoefficient has a negative sign “−”.

In the meantime, in binarization of the transform coefficient sign forthe current block, transform coefficient sign prediction may be used.

In the transform coefficient sign prediction, the signs of N non-zerotransform coefficients in the transform coefficient group, wherein N isa positive integer, are predicted. The case where the actual signmatches the prediction sign is indicated by a value of “1”, and the casewhere the actual sign does not match the prediction sign is indicated bya value of “0”. The transform coefficient sign prediction may beperformed on a per transform coefficient group basis.

For example, transform coefficient sign prediction may be performed witha combination having the most optimum cost among combinations (2Ncombinations) of N coefficient signs to be predicted. Herein, the costof the sign combination may be obtained from the similarity between thedata, obtained by inverse-transforming the current transform coefficientgroup with the corresponding combination, and the neighboringreconstructed image.

[D3-3] Transform Coefficient Absolute Value Binarization

In performing transform coefficient absolute value binarization for thecurrent block, the transform coefficient absolute value binarization maybe performed using at least one method among transform coefficientbinarization based on absolute value comparison, transform coefficientbinarization based on exponential scale absolute value comparison, andthe residual transform coefficient absolute value binarization.

[D3-3-1] Transform Coefficient Binarization Based on Absolute ValueComparison

The transform coefficient binarization based on absolute valuecomparison may be performed on a per transform coefficient group basisor a per transform coefficient basis, or may be performed when thetransform coefficient presence indicator is 1.

The transform coefficient binarization based on absolute valuecomparison may be performed using Expression 1 and a positive integer Nas follows.

Abs(coeff.)>K, K={1, . . . , N}  [Expression 1]

For example, when N is 2, the transform coefficient binarization basedon absolute value comparison is performed as shown in FIG. 30.

For example, K may be 2N or 2N−1. Herein, when K is 2N, the transformcoefficient absolute value binarization is performed by comparing theabsolute value of the transform coefficient with the value of 2, 4, 6, .. . , and 2N. In the meantime, when K is 2N−1, the transform coefficientabsolute value binarization is performed by comparing the absolute valueof the transform coefficient with the value of 1, 3, 5, . . . , and2N−1.

In the meantime, according to the above-described scanning method, onlyI transform coefficients may be subjected to the transform coefficientbinarization based on absolute value comparison. Herein, I may be apositive integer.

[D3-3-2] Transform Coefficient Binarization Based on Exponential ScaleAbsolute Value Comparison

The transform coefficient binarization based on exponential scaleabsolute value comparison may be performed on a per transformcoefficient group basis or a per transform coefficient basis, or may beperformed when the coefficient presence indicator is 1.

The transform coefficient binarization based on exponential scaleabsolute value comparison may be performed using Expression 2 andpositive integers a and N as follows.

Abs(coeff.)≥a ^(K) , K={1, . . . , N}  [Expression 2]

For example, when a is 2 and N is 3, the transform coefficientbinarization based on exponential scale absolute value comparison isperformed as shown in FIG. 31.

In the meantime, according to the above-described scanning method, onlyI transform coefficients may be subjected to the transform coefficientbinarization based on absolute value comparison. Herein, I may be apositive integer.

In FIG. 31, the value of Abs(coeff.) may be the absolute value of thetransform coefficient level. Herein, the transform coefficient level maybe the result of transform and quantization.

As shown in FIG. 31, when a is 2 and N is 3, the transform coefficientpresence indicator, an indicator indicating the case where the absolutevalue of the transform coefficient level is equal to or larger than 2,an indicator indicating the case where the absolute value of thetransform coefficient level is equal to or larger than 4, and anindicator indicating the case where the absolute value of the transformcoefficient level is equal to or larger than 8 are encoded/decoded.

In this case, when the transform coefficient presence indicator has avalue of true (or a value of “1”), the indicator indicating the casewhere the absolute value of the transform coefficient level is equal toor larger than 2 is encoded/decoded. Further, when the indicatorindicating the case where the absolute value of the transformcoefficient level is equal to or larger than 2 has a value of true (or avalue of “1”), the indicator indicating the case where the absolutevalue of the transform coefficient level is equal to or larger than 4 isencoded/decoded. Further, when the indicator indicating the case wherethe absolute value of the transform coefficient level is equal to orlarger than 4 has a value of true (or a value of “1”), the indicatorindicating the case where the absolute value of the transformcoefficient level is equal to or larger than 8 is encoded/decoded.

[D3-3-3] Residual Transform Coefficient Binarization

The residual transform coefficient binarization may be performed on aper transform coefficient group basis or a per transform coefficientbasis, or may be performed when the coefficient presence indicator is 1.

The residual transform coefficient binarization may be performed byvarious binarization methods.

For example, the residual transform coefficient binarization may beperformed using a truncated rice binarization method.

For example, the residual transform coefficient binarization may beperformed using a K-th order Exp_Golomb binarization method.

For example, the residual transform coefficient binarization may beperformed using a limited binarization method.

For example, the residual transform coefficient binarization may beperformed using a unary binarization method.

For example, the residual transform coefficient binarization may beperformed using a truncated unary or truncated binarization method.

In the meantime, the binarization method may be determined according tothe value of the residual transform coefficient.

For example, the residual transform coefficient which is equal to orsmaller than a value of a positive integer c is subjected tobinarization using the truncated unary binarization method, and theresidual coefficient which exceeds the value of c is subjected tobinarization using the K-th order Exp_Golomb binarization method.

In the meantime, the binarization method may be determined according tothe scanning order.

For example, when the residual transform coefficient is subjected tobinarization using the K-th order Exp_Golomb binarization method, thevalue of K is increased or decreased according to the scanning order.

On the basis of the encoding parameter (for example, at least one amongthe slice type, the tile group type, the encoding mode, the intraprediction mode, the inter prediction mode, the value of the transformcoefficient, and the size/shape of the current block), the transformcoefficient binarization method may be determined on a per transformcoefficient basis.

For example, the transform coefficients belonging to the low frequencymay be subjected to exponential scale absolute value comparisonbinarization, and the remaining transform coefficients may be subjectedto the transform coefficient binarization based on absolute valuecomparison.

For example, the transform coefficient having a low quantizationparameter (QP) may be subjected to the exponential scale absolute valuecomparison binarization, and the remaining transform coefficients may besubjected to the transform coefficient binarization based on absolutevalue comparison.

On the basis of the encoding parameter (for example, at least one amongthe slice type, the tile group type, the encoding mode, the intraprediction mode, the inter prediction mode, the value of the transformcoefficient, and the size/shape of the current block), the transformcoefficient binarization method may be determined on a per block basis.Herein, the block may be the transform coefficient group.

For example, when the current block is in the intra prediction mode, thetransform coefficient binarization based on exponential scale absolutevalue comparison is performed. When the current block is in the interprediction mode, the transform coefficient binarization based onabsolute value comparison is performed.

For example, in the case where the current block is in an N×M size, whenthe minimum value (min(N, M)) among M and N or the maximum value (max(N,M)) among M and N is larger than a predefined K (wherein, K is apositive integer), the transform coefficient binarization based onexponential scale absolute value comparison is performed, and otherwise,the transform coefficient binarization based on absolute valuecomparison is performed.

FIG. 32 is a flowchart illustrating a method of decoding an imageaccording to an embodiment of the present invention.

Referring to FIG. 32, an apparatus for decoding an image may determinethe zero out region within the current block at step S3210.

Specifically, when the width or height of the current block is largerthan a first predefined size, a region of which the size is equal to orlarger than the first predefined size within the current block isdetermined as the zero out region. Herein, the first predefined size maybe 32.

Further, the zero out region may be determined on the basis of the typeof frequency transform of the current block. Specifically, when the typeof frequency transform of the current block is DST-7 or DCT-8, a regionof which the size is equal to or larger than a second predefined sizewithin the current block is determined as the zero out region. Herein,the second predefined size may be 16.

On the other hand, when the type of frequency transform of the currentblock is DCT-2, a region of which the size is equal to or larger than athird predefined size within the current block is determined as the zeroout region. Herein, the third predefined size may be 32.

Further, the apparatus for decoding the image may partition the regionexcept for the zero out region within the current block on a pertransform coefficient group basis at step S3220.

Herein, the size of the transform coefficient group may be determined onthe basis of the width and the height of the current block.Specifically, when the width or height of the current block is smallerthan a fourth predefined size, the size of the transform coefficientgroup is determined to be a fifth predefined size. When the width andthe height of the current block is larger than the fourth predefinedsize, the size of the transform coefficient group is determined to be asixth predefined size. Herein, the sixth predefined size may be 4, andthe fifth predefined size may be 2.

In the meantime, the shape of the transform coefficient group isdetermined to be a non-square shape when the area of the current blockis larger than a predefined area and the shape of the current block is anon-square shape. Herein, the predefined area may be 8.

Further, the apparatus for decoding the image may decode the transformcoefficient on a per transform coefficient group basis at step S3230.

The method of decoding the image has been described above with referenceto FIG. 32.

A method of encoding an image of the present invention may be describedsimilarly to the method of decoding the image described with referenceto FIG. 32, so that a redundant description will be omitted.

The bitstream generated by the method of encoding the image of thepresent invention may be temporarily stored in a recording medium.

The above embodiments may be performed in the same method in an encoderand a decoder.

At least one or a combination of the above embodiments may be used toencode/decode a video.

A sequence of applying to above embodiment may be different between anencoder and a decoder, or the sequence applying to above embodiment maybe the same in the encoder and the decoder.

The above embodiment may be performed on each luma signal and chromasignal, or the above embodiment may be identically performed on luma andchroma signals.

A block form to which the above embodiments of the present invention areapplied may have a square form or a non-square form.

The above embodiment of the present invention may be applied dependingon a size of at least one of a coding block, a prediction block, atransform block, a block, a current block, a coding unit, a predictionunit, a transform unit, a unit, and a current unit. Herein, the size maybe defined as a minimum size or maximum size or both so that the aboveembodiments are applied, or may be defined as a fixed size to which theabove embodiment is applied. In addition, in the above embodiments, afirst embodiment may be applied to a first size, and a second embodimentmay be applied to a second size. In other words, the above embodimentsmay be applied in combination depending on a size. In addition, theabove embodiments may be applied when a size is equal to or greater thata minimum size and equal to or smaller than a maximum size. In otherwords, the above embodiments may be applied when a block size isincluded within a certain range.

For example, the above embodiments may be applied when a size of currentblock is 8×8 or greater. For example, the above embodiments may beapplied when a size of current block is 4×4 or greater. For example, theabove embodiments may be applied when a size of current block is 16×16or greater. For example, the above embodiments may be applied when asize of current block is equal to or greater than 16×16 and equal to orsmaller than 64×64.

The above embodiments of the present invention may be applied dependingon a temporal layer. In order to identify a temporal layer to which theabove embodiments may be applied, a corresponding identifier may besignaled, and the above embodiments may be applied to a specifiedtemporal layer identified by the corresponding identifier. Herein, theidentifier may be defined as the lowest layer or the highest layer orboth to which the above embodiment may be applied, or may be defined toindicate a specific layer to which the embodiment is applied. Inaddition, a fixed temporal layer to which the embodiment is applied maybe defined.

For example, the above embodiments may be applied when a temporal layerof a current image is the lowest layer. For example, the aboveembodiments may be applied when a temporal layer identifier of a currentimage is 1. For example, the above embodiments may be applied when atemporal layer of a current image is the highest layer.

A slice type or a tile group type to which the above embodiments of thepresent invention are applied may be defined, and the above embodimentsmay be applied depending on the corresponding slice type or tile grouptype.

In the above-described embodiments, the methods are described based onthe flowcharts with a series of steps or units, but the presentinvention is not limited to the order of the steps, and rather, somesteps may be performed simultaneously or in different order with othersteps. In addition, it should be appreciated by one of ordinary skill inthe art that the steps in the flowcharts do not exclude each other andthat other steps may be added to the flowcharts or some of the steps maybe deleted from the flowcharts without influencing the scope of thepresent invention.

The embodiments include various aspects of examples.

All possible combinations for various aspects may not be described, butthose skilled in the art will be able to recognize differentcombinations. Accordingly, the present invention may include allreplacements, modifications, and changes within the scope of the claims.

The embodiments of the present invention may be implemented in a form ofprogram instructions, which are executable by various computercomponents, and recorded in a computer-readable recording medium. Thecomputer-readable recording medium may include stand-alone or acombination of program instructions, data files, data structures, etc.The program instructions recorded in the computer-readable recordingmedium may be specially designed and constructed for the presentinvention, or well-known to a person of ordinary skilled in computersoftware technology field. Examples of the computer-readable recordingmedium include magnetic recording media such as hard disks, floppydisks, and magnetic tapes; optical data storage media such as CD-ROMs orDVD-ROMs; magneto-optimum media such as floptical disks; and hardwaredevices, such as read-only memory (ROM), random-access memory (RAM),flash memory, etc., which are particularly structured to store andimplement the program instruction. Examples of the program instructionsinclude not only a mechanical language code formatted by a compiler butalso a high level language code that may be implemented by a computerusing an interpreter. The hardware devices may be configured to beoperated by one or more software modules or vice versa to conduct theprocesses according to the present invention.

Although the present invention has been described in terms of specificitems such as detailed elements as well as the limited embodiments andthe drawings, they are only provided to help more general understandingof the invention, and the present invention is not limited to the aboveembodiments. It will be appreciated by those skilled in the art to whichthe present invention pertains that various modifications and changesmay be made from the above description.

Therefore, the spirit of the present invention shall not be limited tothe above-described embodiments, and the entire scope of the appendedclaims and their equivalents will fall within the scope and spirit ofthe invention.

INDUSTRIAL APPLICABILITY

The present invention may be used in an apparatus for encoding/decodingan image.

1. A method of decoding an image, the method comprising: determining azero out region within a current block; partitioning a region except forthe zero out region within the current block, on a per transformcoefficient group basis; and decoding a transform coefficient on the pertransform coefficient group basis.
 2. The method of claim 1, wherein atthe determining of the zero out region, when a width or a height of thecurrent block is larger than a first predefined size, a region of whicha size is equal to or larger than the first predefined size within thecurrent block is determined to be the zero out region.
 3. The method ofclaim 1, wherein at the determining of the zero out region, thedetermining is based on a type of frequency transform of the currentblock.
 4. The method of claim 1, wherein at the determining of the zeroout region, when a type of frequency transform of the current block isDST-7 or DCT-8, a region of which a size is equal to or larger than asecond predefined size within the current block is determined to be thezero out region.
 5. The method of claim 1, wherein at the determining ofthe zero out region, when a type of frequency transform of the currentblock is DCT-2, a region of which a size is equal to or larger than athird predefined size within the current block is determined to be thezero out region.
 6. The method of claim 1, wherein a size of thetransform coefficient group is determined on the basis of a width and aheight of the current block.
 7. The method of claim 1, wherein when awidth or a height of the current block is smaller than a fourthpredefined size, a size of the transform coefficient group is determinedto be a fifth predefined size, and when the width and the height of thecurrent block is larger than the fourth predefined size, the size of thetransform coefficient group is determined to be a sixth predefined size,wherein the sixth predefined size is larger than the fifth predefinedsize.
 8. The method of claim 1, wherein a shape of the transformcoefficient group is determined to be a non-square shape when an area ofthe current block is larger than a predefined area and a shape of thecurrent block is a non-square shape.
 9. A method of encoding an image,the method comprising: determining a zero out region within a currentblock; partitioning a region except for the zero out region within thecurrent block, on a per transform coefficient group basis; and encodinga transform coefficient on the per transform coefficient group basis.10. The method of claim 9, wherein at the determining of the zero outregion, when a width or a height of the current block is larger than afirst predefined size, a region of which a size is equal to or largerthan the first predefined size within the current block is determined tobe the zero out region.
 11. The method of claim 9, wherein at thedetermining of the zero out region, the determining is based on a typeof frequency transform of the current block.
 12. The method of claim 9,wherein at the determining of the zero out region, when a type offrequency transform of the current block is DST-7 or DCT-8, a region ofwhich a size is equal to or larger than a second predefined size withinthe current block is determined to be the zero out region.
 13. Themethod of claim 9, wherein at the determining of the zero out region,when a type of frequency transform of the current block is DCT-2, aregion of which a size is equal to or larger than a third predefinedsize within the current block is determined to be the zero out region.14. The method of claim 9, wherein a size of the transform coefficientgroup is determined on the basis of a width and a height of the currentblock.
 15. The method of claim 9, wherein when a width or a height ofthe current block is smaller than a fourth predefined size, a size ofthe transform coefficient group is determined to be a fifth predefinedsize, and when the width and the height of the current block is largerthan the fourth predefined size, the size of the transform coefficientgroup is determined to be a sixth predefined size, wherein the sixthpredefined size is larger than the fifth predefined size.
 16. The methodof claim 9, wherein a shape of the transform coefficient group isdetermined to be a non-square shape when an area of the current block islarger than a predefined area and a shape of the current block is anon-square shape.